Why would people see this iMac from any different angle than any other iMac? Plenty of situations where no one would see the back. I just like it because it's iconic. Even the original colorful G3s said "iMac" on the front.
Probably best ask Apple, but that is what their presentation seemed to say. Personally though, the only person who sees the front of my computer is me. All my colleagues see of it is the back. They'll hopefully like the blue color and logo on mine when it gets here.
Otherwise, I can't answer for Apple's choices. All I can say is that personally I could really not care less what they did in the past. It's a new product, I don't see why there is a reason it has to conform to someone's idea of a rule of come kind. But you'll have to ask them for their reasoning.