It is strange. Perhaps the goal isn't to create a theme for all the lines; the designer might have simply thought that the iMac was looking tired. There doesn't have to be a coherent theme to Apple's products. As long as we know what an iMac looks like, what a macbook looks like, what a Mac Pro looks like, etc, the individual products need only one guiding principle: they must be attractive. So far as I can tell, none of Apple's products is unattractive. Thus, the current designs are doing what they were intended to do.
PS: I like being quoted, but I also like to be cited


JK