The point is, there isn't (and will NEVER, and not in the euphamistic "..well, they've said that before" sense, but the REAL, NEVER, sense) be a need to address more that 2^64 chunks of memory.
EVER.
So, a 32 bit machine usually means 2 things: 32 bit instructions and a 32 bit address space (note that I said usually...this is the conventional sense of the term). So, yes, there will be computers with more that 64 bit instructions (I mentioned VLIW), and it is concievable some other ISA would need huge-ass instructions. But the point is, you'll never need to address that much memory.
EVER.