I think you're misunderstanding something. 32-Bit software does, of course, run just fine under 64-bit Windows. It's just that 32-bit software cannot address and use many of the resources of a 64-bit system.
Correct. There's no need to write smaller 32-bit programs into 64-bit code. They don't need and usually wouldn't use the full resources of a 32-bit system. But large graphical programs like the cartographic applications that I named would perform much better if they had access to memory over 4 GB and the other resources that a 64-bit system has to offer,on PC, we got many 32 bit programs still running. Although most of these are small and would not benefit being coded in 64 bit.
Servus,