Yes - a specific error message would be much more helpful than a vague reference to x64.
And if the concept of compatibility only extends to "It won't plug and play like on my game console".
they yes there would be many PC games that are incompatible, and always have been, even on XP.
Technically the DRM may be incompatible, or there may be some other issue, but the game itself is
very likely compatible.
Of course without knowing the name of the game we can only speculate (even then speculation
may be necessary as there are a lot of games out there), but I've only come
on one game that will not run on my Win7 64bit machine - Beyond Good and Evil (original CD version), and this is also because of a DRM conflict. The only reason I have not been able to get it running is there no one has made a noCD fix for this particular game.
It's well known that DRM (including GFWL) has caused more problems for honest people who purchase games than it does pirates, but all gamers can be thankful hackers are there to provide us with fixes to make these games playable. I wouldn't be surprised the gaming industry is also quietly thankful, otherwise many more people would give up on PC games in disgust at the rude treatment dished out to
honest people by the game publishers and their copy protection systems.
If regard to the much publicized Compatibility Mode. It is rarely necessary. I've only used it on
perhaps half a dozen of well over 100 games. Even then it was only as a precaution.
btw - I've just recently discovered that Integrated Graphics (specifically Intel HD4000) is a hit and
miss affair regarding it's compatibility. I'm not talking about capability to run various games, more
driver incompatibility with a wide range of games, both recent and older, that run fine on dedicated
graphics cards.