I was initially disappointed that a large design component of iOS 7 is seemingly being withheld from the 3rd gen ipad.
One thing I realized, however, that accounts for why we see translucency in certain places but not others, has to do with whether the blurred area behind is dynamic or not. For example, the translucent dock, and the translucency that appears behind the home screen icons when multitasking, are always going to be static wallpaper elements. The GPU only has to calculate the blur once, and then slide things around overtop of it. By contrast, the notification centre and Control Center shades are able to slide down over arbitrary content (websites, running apps, etc). So the argument can be made that processing overhead was the deciding factor.
All that said, I have to question the use of such a heavy post processing effect (that it can't even run on 1-generation old hardware) as a fundamental aspect of the OS visual design. Personally, I think translucency and parallax everywhere aesthetic is going to become dated more quickly than the skeumorphism that everyone has been complaining about.
