rampancy: It's a matter of opinion in terms of what people want to do with the platform they choose.
Navagon: Yes. but in this case it's plainly established that they want to play games on their computer. Although that said, I still can't think of one thing a Mac can do you can't do with a Windows PC... other than hand over considerably more money.
Usability is different but technical differences are rather limited. Photo and graphics enthusiast like to pretend they are still somehow superior, but its mostly an ego thing. But there is something to be said about someone wanting a system with stricter hardware and software selections though. In the sense that there are fewer things you can do to a mac there is less to go wrong. People are willing to pay for a more dependable ride. I wouldn't pay it, but then thats why I run linux. I don't want pay for a mac or even windows . The only thing I cant do is play the full windows spectrum of games.
Now if that didn't HAVE to be the case would I be interested. Yes. I would be interested in being able to do everything. And given that that is a technical possibility AND developers are making games with other versions, then its not crazy to be interested in having them offered by a company that likes to offer extras.
There are two kinds of games people need to think about when asking GOG to offer other games. There are games with linux/mac versions, and games without. Asking GOG to some how make old games work on other OS'es is unrealistic. Even if it were possible in a given instance they would be forced to offer support because it would end up being their product.
Asking for new games like Trine that clearly have a linux versions available is not asking for something wildly unrealistic. There is the support issue which is very off putting for someone not wanting to get their hands all dirty supporting other OS'es. I don't think they should offer support for them, but toss them in and say "there you weirdos go. No support. Go bug the dev's.I'd be fine with that."
One problem I see is that some of these devs is that they seem to be using it as a way to get people to buy it from a specific place. Kind of a "Buy it from us get the linux version." Its hard to offer something they want to keep for themselves. Ultimately I think it should be up to the developers to offer other versions to people that have purchased their game. ID did this repeatedly. The runtime installers for Q3 and RTCW were available for linux and PC on their own website. All you had to do was have the game data files and you could run your game in both environments. Frankly I'm a little off put that devs aren't doing this now even though they have created both versions. Don't try and sell me two copies because I have two OS'es,
BTW people there is a wishlist for this and for a MAC/Linux users forum in the wishlist. Go vote.