I also don't see iOS and Android having much of a usability gap. At this point, they have very similar feature sets, and the UX is fairly well-polished, even on Android -- where yes, it took them a lot longer to get there. For the most part, if you think that either platform has bad UX, it's probably just because you've used the other one for so long, and you're used to it. (I don't think iPhone usability is bad, but on the rare occasion I do something on my wife's iPhone, I find it frustrating because it just works differently than my Android phone.)

At this point I think most (US; can't speak for other countries) iPhone users are there mainly because they've always been there, and there's fairly strong lock-in and switching costs. And iPhones are still something of a status symbol, not to mention unnecessary Apple-created problems like the "blue bubble envy" nonsense.