[zokier]

AMD64 also included a lot more registers, and has some extensions to the instruction set. It also makes a baseline for other features like SSE, as all CPU:s supporting AMD64 are relatively modern. Also having larger address space to work with may affect some design decisions.

So while you can write 64-bit code just like 32-bit code, it's bit like saying that writing c++ is no different than writing c.