actually i disagree on that, even 32bit progs on x64 can benefit from largeaddressaware compiler settings, and disc caching, network, video can benefit as the os shifts them to high areas, leaving more space available to the process.. pid for example is faster running on a 64bit os compared to running on the same pc in a 32 bit os... And some x64 apps are quite quicker too like winrar...its considerably quicker unraring (and raring) on x64.. slowly but surely x64 is becoming more common and for games this will be evident in the next consoles which will more than likely be x64 and then game ports will go x64, so going x64 now (and having more than 4gig ram) may future proof you a lot more than investing in a 32bit system
all of my pc's at home and in work are x64 and i have not had any problems with 32bit programs... 16bit and lower code wont run but thats what dosbox is for