There are lots of 32 bit apps. that don't run on 64 bit.
Usually they are programs that require drivers
- disk management apps. for example - the interesting an useful ones.
Fortunately, many of those now make 64 bit compatible versions. ( with 64 bit drivers )
Depending on your requirements it may not bother you.
That's why so many people dual boot , or run another o/s in a VM - so they can use certain apps. Sometimes that isn't because of the bitness , but because it is won't run properly (or at all ) in 7 , let alone 64 bit.