The theory that all apps must/should look the same seems like common sense until you surf the net (including UT) and you quickly see that there seems to be another dynamic at play: "make your interface as different as possible so that it will stand out from the crowd".
Can these two be reconciled? Who is the arbiter of what looks "right"? Don't we sometimes insult people's intelligence by assuming that they cannot handle anything as weird as a non rectangular command button? How come Microsoft can change the look of buttons etc and that's OK but not the rest of us? BTW these are all rhetorical questions - just venting...