Uh, you can hardly blame Microsoft for lower framerates in EU when Mindark don't officially support Vista. The fact other DirectX games perform the same or better in Vista suggests Mindark are at fault. Particularly given such an enormous FPS different like that.
And yes, I have tried Bioshock (for example) on this computer running XP (32-bit) and also after I installed Vista x64, and I get around 20fps more on Vista. This is hardly news though because other users have reported the same, and reliable benchmark reports out there confirm it too.
The fact is that with a dual-core (45nm) processor, 4GB of fast RAM, a good NVidia card, and Vista x64 (which performs around 10% better than Vista 32bit donchya know) yes indeed all my games run the same or better than they did under XP -- with the exception of EU which is no surprise because Vista is not supported --
but if you want to convince yourself otherwise, be my guest.
If it performed worse, I would simply revert to XP, but it doesn't so I won't. Now, if I was still using my old Pentium 4 3.8 Ghz single core processor, I might agree with you because Vista has certainly upped the hardware ante, and it seems to hate two year old and/or single core computers. But that kind of system is hardly a decent gaming rig even with XP installed.