From Steve's original iPhone presentation in 2007: these devices already run Mac OS X. Of course, iOS is a version of Mac OS X that lacks things that mobile devices don't use (such as all of Aqua), and adds things that they do (like Cocoa Touch); and, it runs on ARM chips instead of x86.

But the answer to the article is simple: of course the Mac desktop doesn't belong on very small mobile devices, which is why iOS exists.