Why did the Win64 team choose the LLP64 model?

Over on Channel 9, member Beer28 wrote, "I can't imagine there are too many problems with programs that have type widths changed." I got a good chuckle out of that and made a note to write up an entry on the Win64 data model. The Win64 team selected the LLP64 data model, in which all integral types remain 32-bit values and only pointers ex...