Honestly this isn't a big deal it's massively overstated. OS X managed to pull of Aqua and MS managed to pull off Aero both with arbitrary UI sizing.
I feel this point is only stated by people who came to UI when they only had to worry about 1 size and then were shocked at the idea of treating the UI as anything other than a Photoshop flat.
The difference is also (I think) the average size of teams which made the apps. iOS has started the boon of one developer per app. Before it was of course done, but the scale is not comparable.