Prices will decrease for the devices or brands that no one cares about. Brands are important and the quality brands will always be able to charge a premium.
So Apple may not be able to get away with 40+% margins but they won't be competing with dirt cheap stuff that is commoditized.
Note how they managed to remain at the top of the mp3 player market long after it became commoditized. That market dropped when they killed it with the iphone.
Well, it also depends if their products can continue to be perceived as a "premium" product over their competitors.