I think at least some of it is the Windows on Windows stuff to allow 64 bit machines to run both 32 and 64 bit software. Weren't the 32 but versions of Win7 abo

I think at least some of it is the Windows on Windows stuff to allow 64 bit machines to run both 32 and 64 bit software. Weren't the 32 but versions of Win7 about half the size of the 64 bit ones? There's still a lot of size growth over time, of course.