You don't have to look very hard to find game's in GOG's catalogue that don't suppport win7 yet.
Are GOG continuing their support of these games? Do they intend to fix their catalogue or are they just going to 'forget' some of them?
GOG have been progressively working through the catalogue, but it's probably not a top priority for them compared to things like securing new titles for the catalogue because all but a handful of GOG releases work perfectly on Windows 7 (since its compatibility is largely identical to Vista).
Many other services never change their store pages at all (so will continue listing XP or whatever as the newest officially supported version) and this doesn't stop people buying older games from them, so I'd imagine GOG customers are generally open to buying games that don't specifically say they are compatible. If you're wanting to know whether a particular GOG release works on Windows 7 you can ask around on its forum, and the answer is almost always "yes".
GOG will have to go through this all over again with the upcoming Windows 8, and as with Windows 7 it's to be expected that all but a handful of GOG releases will work perfectly without changing anything.