Apple really didn't have any legacy support or enterprise clients to speak of. Apple also included a Classic Mac emulator in early versions of OSX to allow programs to keep running while developers created new ones, similar to the classic Desktop mode.

When iOS was introduced, Apple had existing OSX customers. Microsoft does not have so many tablet enterprise clients that have to drag the desktop metaphor along just to appease them. Their enterprise clients didn't have to dictate what the XBox was. Tablets could be just as free of legacy as it.

ARM tablets won't have the legacy desktop. Only x86 installs will have that, because that's where the legacy support is needed.