Tim Cook describing the Surface as a “sorta-tablet, sorta-PC” thing, reminds my Steve Ballmer mocking the iPhone few yrs ago. In both cases I find it immature and short-sighted.
From a hardware perspective being half and half is fine, I think the criticism of the surface is that the interface and software is optimised for neither paradigm and the device suffers as a result. Apple may well release a Mac Air with a touchscreen, but I doubt it will run in IOS mode and in OSX mode, it will more likely pick one and stick with it.