This discussion usually comes down to what exactly it is GOG should do, and by what criteria.

Some e.g. feel GOG should not sell any games that are missing some non-English language version or the Mac/Linux version, and some even feel GOG should not sell a game if it is missing achievements (while the Steam version has them).

I personally feel that in such cases all we can expect from GOG is to clearly mark with the games what languages and OSes and features (like achievements) are supported in the GOG version, and then everyone can make their personal purchase decision based on that. For instance, as I couldn't care less whether a game has non-English localizations or Mac support or whether it has achievements, I want to be able to to buy such games that may be missing them. Others may decide differently.

Would you e.g. refuse to buy some GOG game that you've been eagerly waiting for if I told you that it is missing Finnish language localization (while the original retail or Steam version has it)? You probably couldn't care less, and I am not expecting you to care.

With missing updates it is more complicated as GOG is usually not even aware whether they have the latest version of each and every game in the store, and if not, what exactly is missing (e.g. critical or non-critical updates).

I just thought about it... and realized that I'm not a professional business/market analyst and have no inside information about GOG as a company.

I know it is unfair not to receive the same treatment when you pay for the same game, I spoke with some developers and the process to update games in gog is slower than in other platforms but at the same time it is more secure, they control every installment of the process.
I'm not a professional market analyst either, but I agree that gog should add some legal clause that forces developers to update the game if it has a stable version within 30 days, to offer a better service to all the customers, I know that many do not consider that they are necessary other localizations to other languages apart from english but that helps to contribute increase the market of GOG, not many people are fluent in English (myself included) and had another localization that was included in the game in other plataform and arbitrarily excluded in GOG... I'm not a professional but I don't think that is good for the buisness. If it's part of the game, why don't have it here too?? I'm not against a bad update being skipped, but a good one or a critical one is unacceptable, not to the point to remove the game, but at least should talk to the developers about it.