I know it sounds plausible, especially considering the ugly hacks that are revealed on The Old New Thing. But I don't think there's ever been any proof, or even

I know it sounds plausible, especially considering the ugly hacks that are revealed on The Old New Thing. But I don't think there's ever been any proof, or even good examples of it. Management, friction between departments and time wasted on visual overhauls could easily be bigger factors than a few thousand (or millions) lines of ugly code maintained for backwards compatibility. Empirically, the iCloud reboot is still meh. iMovie (cleanly rewritten one version ago) is averaging at 3 stars on the Mac App Store, with especially devastating reviews in the German MAS. On the other hand, iOS 7 is moving very fast while being one of the products where Apple cares a lot about backwards compatibility.