And really, how similar every non-notebook/desktop Apple product has been to each other one. Design-wise, the iPhone was just an iPod with a bigger screen; iPod touch/nano/other variations are obviously just an iPhone in different sizes; the watch is just the iPod nano on a wristband; iPad is a bigger iPhone. Apple hasn't released a fundamentally new design idea in over a decade.
On the one hand, the consistency of physical design is its own type of branding and creates solid brand recognition. On the other hand, the UI/UX that transformed interacting in the digital world from using keyboards and mice to using our fingers on touch screens is already old. Apple really has no need to be creative since they are still profiting from their slight modifications. But the next big, real revolution in personal computing design and usage will need to be more than a glass rectangle with slightly better curved edges.