There's a very fine line from Linux or Mac OS falling into the same trap though... I remember way back before it was common to use GDM or KDM, I used to log in as root, then run startx to get a friendly interface going on. Now THAT is a security nightmare beyond anything Windows has! Thankfully I wasn't on any significant Internet connection at the time. Technically speaking, all a distribution has to do is say "this sudo password thing is confusing to new users. Let's just present them with an OK dialog box instead!" Then the next step is eliminating the dialog box and then doing it in the background. The next step is IE :). It can be a very very short slide from a secure system to a playground for hackers, all for convenience stake.
Hopefully we can trust companies like Canonical or Apple not to do that, though. I like to think we can. Actually I have good hopes for Microsoft. They sure ain't perfect but we've come a LONG way from IE 4 on Win98.

I'm guessing that while security may be a minor consideration for the folks at Google, the main reason for this is most likely a PR attack against MS. A massive part of Microsoft's sales and a major contributing factor to the MS monoculture is the use of MS products in businesses, and with this move Google is sending a message to every other business out there that MS products are not a necessity for a large company. As Google is starting to move into the software business confrontation with MS is inevitable and I think that this move away from MS products is just an opening volley in what's going to end up being a pretty major battle between Google and MS.

I'm with DarrkPhoenix on this one.
The stated rationale is a strange one, given that OS X remains an option.
OS X's security strategy is mostly security-by-obscurity. That's a viable defense against commercial hackers interested only in sheer numbers of compromised systems and indifferent to particular targets. It's a really lousy defense against government hackers targeting organizations. Only fundamentally sound security will thwart these guys.
I'm betting this is a political move. It's a great opportunity to turn the lemons of that recent Chinese intrusion into the lemonade of a big media/rhetorical win against Microsoft.
I also think that Apple is a red herring here.
Google is dumping Microsoft because they are pushing cloud based apps. They are saying you don't need those legacy apps, as the greater SaaS community has you covered. This is a direct attack on Microsoft Windows and Office, and this can/will have an appeal outside of just Google. They are making a play at corporate customers. This is a very big deal.

Every little bit helps. If running a Linux or Unix based operating system even helps a little, then it's technically a bit more secure. They shouldn't let it get to that point, but it's something I guess.

Only, in short, it isn't.
To expand on that, Google, is more of a nix shop. So standardizing on nix makes sense to them. It also in their eyes lowers the attack profile by lowering the amount of OS's their internal support staff have to support. Sure, Windows 7 x64 has far more security technology's then OSX. thats a fact, not really disputable.
And here's where I think the Mac OS X thing is crazy: programs on Windows 7 are harder to exploit than they are on Mac OS X due to Windows' superior technical protections. Browser sandboxing, fully-fledged ASLR and DEP, secure heaps; these features conspire to make exploitation of flaws much harder on Windows than on Mac OS X.
If you're truly worried about 0days and targeted attacks, you'd be crazy to use Mac OS X.
Mac OS X does in fact have an interesting sandboxing facility, it's just that Apple doesn't bother to actually use it for anything that should be sandboxed (Safari, Mail), and hasn't documented the feature at all. It looks like it has the potential to be very powerful (sandbox configuration is configured using scheme scripts, providing features similar to AppArmor), but that's all it is: potential.
I believe Apple also stubs out FreeBSD's jail functionality, so that's not an option, which is also a pity.
Windows offers arguably the least advanced features in this area (MIC does provide a kind of sandboxing, but it doesn't provide the ability to, for example, prohibit certain system calls or limit socket access), but, when compared to Mac OS X and typical Linux distributions, yields the most benefit from the features it does have. A rare case of Microsoft actually bothering to use new platform capabilities.
Sadly, this doesn't extend to, say, Windows Live Mail or Outlook; it's only used in Internet Explorer.

Not at all. They're being targeted. These aren't random attacks. So in the case of Mac OS, this leaves them completely open.

Now what the hell does having Windows on their employees' PCs have anything to do with their webservers getting jacked?

IIRC, the server hack happened because one of their employees got their laptop hacked while mobile. Server access passwords and the like were stolen.

You're focusing almost entirely on OS X when the article lists Linux as one of the options. Do you have similar feelings towards it?

Then thats an educational / HR problem, not an IT one. What in the name of fuck was this person doing with passwords written down in the first place? Thats the very first security vulnerability that people should be taught to avoid

I'm not that informed when it comes to actual Linux capabilities/vulnerabilities when it comes to security to comment on that unfortunately because it ties in the way the apps interact with the kernel/OS subsystems which represent the main points of entry. I guess they could use RHEL with full-SELinux to be as protected as possible but further than that I have no idea.
I know for a fact that a properly configured and administered Windows 7 (I guess even Vista as the respective underlying architecture hasn't changed that much compared to the transition between XP and Vista) box is just as safe as a properly configured and admin'd Linux box.
As I said, in my opinion, Google is dumping Microsoft because they are pushing cloud based apps. They are just using the Aurora hacks incident as a PR push for this.
We also need to keep in mind that the Aurora hacks were targeted. When you're aiming hacks at particular companies, your exploit selection criteria change.
For normal mass-market attacks, you want an exploit that's cheap and widely useful. As a general rule, this means you target Windows and Internet Explorer, and it means that you use patched exploits rather than 0days.
But the Aurora attacks were aimed at specific companies. That changes the selection criteria somewhat. You now have to account for the organization's security policies and platform choice. So, for example, if you know the organization keeps its machines up-to-date, you'll need to discover (or purchase) a 0day flaw. That way you can evade virus scanners and patches.
So as a response to your question, I don't know if Linux is better at security than OS X (I tend to answer yes though due to the SELinux implementation) but the issue is that a determined hacker (team), given enough time and resources can get in no matter the OS. It's just that on certain configurations it takes longer and is more visible. No matter what OS you're using, you aren't safe from a concerted, targeted attack. The whole concept of finding and exploiting a weakness in a specific company's security means no amount of sandboxing, ASLR, DEP or secure heaps is going to keep some hacker from finding either a 0day that works around and/or avoids these measures (XP compatibility mode anyone?) or a worker, who despite all the best efforts, doesn't manage security adequately.
As for an internal view, I don't really see Google employees caring that much (except for those that are involved in app development). The two people I know working at Google told me that engineers are so focused on their projects that their computers themselves hardly matter. They're cranking away on web-oriented projects that have nothing to do with the OS running on their workstation. Their lives are in web browsers, IDEs, and command-line sessions. The apps they build run on various Google-internal OSes. Even within the office, much of the work is effectively done remotely. Take this with a grain of salt as it isn't first hand knowledge but I sincerely trust that this is the case.