Android, the platform has sold a bunch more than iPhone, the phone. Because Android isn't one company's phone, it's the default free OS that phone vendors besides Apple and RIM adopted en masse. Why? Because by getting on board with Android, phone vendors don't have to pay the license fees, and can cut development costs. Plus they can get some pre-built apps for the phone without having to cultivate their own app market.
As far as phones themselves? iPhone sells far in far higher volume than any one Android phone - it just doesn't outsell the whole Android ecosystem. And won't anymore at this point. But the key metric is really how large, robust, and lucrative the platform app markets are. iOS' App Store dramatically outsells the Android Market right now and probably will for the reasonable future. Why? I think part of the reason is the nature of Android itself, and the phones it goes on. Outside of the passionate few, Android mainly is the generic OS you get when you get that phone that's a step up from the old feature phone you had, and there's no iPhone available as an option (or you don't really care one way or another, you just want the phone that's cheapest on a contract and has a web browser and e-mail).
I think the tablet market is a little different, at least to date. First of all, the iPad came to market as really the first fully-formed vision of a viable tablet. And right now just as the competition starts to catch up, Apple does something to jump ahead again. iPad 2 isn't much better (if at all) technically than the Xoom, but they have design in their favor, roughly identical specs, and Apple has a much more mature app ecosystem and about a year's head start.
It'll take a few years for the competition to even out. And meantime, these newer platforms don't really lend themselves to the old Windows ecosystem model where one company dominates and everyone else fights for scraps. Apple sells millions of iOS devices each quarter (over 20 million last quarter), and all those users reinforce each other, buying upgraded devices eventually and also buying apps. Developers make lots of money writing iOS apps. That isn't going away. At least 2, maybe even 3 platforms will likely survive and thrive for a long time to come. Apple's advantage now is that they are building devices for consumers, not so much for engineers. That's part of their DNA and why Android won't ever "win" outright.