Fenixp: Because in this case, Microsoft would actually profit immensely from closing it down and only allowing distribution via store, if they manage to beat apple in convenience.
Oh boy. But even for WinRT applications distributed through Windows Store, you don't have to give Microsoft anything. You can use third party transaction services that aren't connected in any way to Microsoft.
For example, I distribute a game through the Store. The game's firstly in trial mode allowing you to play 1/10th of it. When you want to buy it, the game features its own transaction page and all that, that is not connected to Microsoft in any way. Through the transaction, you pay using some whatever service I support, and I just give you a key that you can insert to unlock the full game. Resulting in Microsoft getting 0 coins. And this is all perfectly legal and supported.
Developers have a huge choice. :p
Fenixp: So yes, GOG would be paying 100 - 160 EUR for links.
Its not like they cannot afford that. They are free to ignore this if they want. They'll gain huge exposure, but hey, who am I to suggest stuff, right?