[millstone]

Aside from universal binaries, Apple's approach to 64 bit also provided a better user experience. Microsoft required you to choose either a 32 bit or 64 bit version of Windows, with the 64 bit version breaking driver compatibility. Apple enabled 64 bit apps to run atop a 32 bit kernel, enabling driver compatibility, at a slight perf cost.

Probably these new ARM machines won't support legacy hardware, though that may not be relevant nowadays.