All the x64 game ports seem to load faster, though. I don't know what that's about. I used to have a theory, but it seems stupid now that I think about it.
I assume what you speak of with the registers is only 'available' ones instead of stuff held by the OS...I'm not a programmer, just a techie, so not exactly clear on that sort of thing. I do know 32 bit has 8 and 64 has 16, but hard numbers don't mean anything if you don't actually know how they're used
I do understand development in general though, and I would expect the gains won't be too visible until more of the Windows environment (MSXML, directx, and whatnot) itself is further optimized for 64 bit, since just about everything ties into certain tools.