You will find that most new rigs coming out will generally lean towards x64 simply because x32 is handled by x64 for Vista and Win 7. As Lord Bob pointed out, it is rare for any programs not able to work under x64 that is written for x32, only the really old legacy programs which most companies have abandoned in favor of new systems and coding methodologies as well as just taking advantage of newer technologies to make up for the need for 'tight' code, for the sake of expediency.
I think the only time you will see systems running on x32, it would be on lean, older systems or systems where you know you can't really meet the demands. Usually places where you have existing hardware but not the budget to upgrade the hardware a bit more, just the OS due to environment requirements. While processors shouldn't be a problem for 3 to 5 year old computers, nor should memory, the time invested in a replacing parts of hardware and OS is more expensive than just simply using an image that will work with the hardware as well as possible legacy issue (Although if you have legacy programs... You would still have problems due to possible changes from OS and software implementations, as I have come to learn where there is a company that still has to use a Windows 95 machine for their out of date, out of product support program they still want to use.)