1. iPhone leads out of the gate.
2. Apple charges a premium.
3. Apple does not license the OS for clones.
4. Google not only licenses the OS, it's completely free, as is their development kit and app store.
5. Apple lacks some infrastructure redundancy and is reliant on ATT and Foxcon, maybe others.
Some differences this time around:
1. Meta standards. There's no longer the Microsoft file formats vs the Apple file formats that locked so much of the world into Windows/Office. These open meta standards eliminate the possibility of lockin. Hence even if Android pulls ahead in market share, it won't have the lockin that Windows had.
2. Apple has fully transitioned from a computer company to an industrial design company. They just happen to specialize in consumer technology (and are not too shabby with the business tech either, thanks to BSD). Most people, consciously or subconsciously, perceive Apple this way as well. Apple owns this niche.
3. Unlike Microsoft, Google actually has a sense of design and aesthetics. Not quite at Apple's artistic level, but, crucially, intuitive, easy to use for noobs, with power-user features under the hood.
I do see Android eventually outselling iPhone simply because of its cost, openess (to handset makers, app devs, and end users), economy of scale, and Google brand.
But I think there's room in this field for both, and no lockin to prevent that. Apple will do fine as the BMW of handsets, I don't see them coming so close to death in that role as they did the last time.