Mark,
Nice post ... this is interesting because Windows environments often ask the same things. Most of which have to do with the hardware, not the O/S itself.
The terms 32-bit and 64-bit refer to the way a computer's processor handles information. In most all cases, the 64-bit version of and O/S will handle data faster, due to the the way it's processed in the hardware.
64-bit is also a term given to a generation of computers in which 64-bit processors were the norm.
(This is why you have had 64 bit processors without actually using 64bit data from the prior o/s..)
64-bit CPUs have existed in supercomputers since the 1960s and in RISC-based workstations and servers since the early 1990s. So in other words, (IBM, Sun, Cray, SGI..etc..)
In 2003 they were introduced to the (previously 32-bit) mainstream personal computer arena, in the form of the x86-64 and 64-bit PowerPC processor architectures.
Without further qualification, a 64-bit computer architecture generally has integer and addressing registers that are 64 bits wide, allowing direct support for 64-bit data types and addresses.
However, a CPU might have external data buses or address buses with different sizes than the registers, even larger (the 32-bit Pentium had a 64-bit data bus, for instance). The term may also refer to the size of low-level data types, such as 64-bit floating-point numbers.
I believe this explains answers to your questions. Let us know if you have more around this. :P
For reference ---
http://en.wikipedia.org/wiki/64-bit