While I agree there were some shakeups, I think it also proves my "major technological change" point. Mac OS to OS X was a major technological change. Went from a pretty, but clunky, single-tasking, OS to a quite advanced UNIX-based multi-tasking OS. UI was the smallest of the changes that happened there. There was also a major processor and architecture change in that story line. Big differences. Having a native app was mandatory to take advantage of a huge jump in capability.