Hi
In my view Android is a great OS, I have an HTC Hero and an HTC Magic. Its great for email, calendar sync via Google Calendar. I like the way I can leave a Twitter app running and new twitter messages show on the notifications bar in the same way as SMS or emails would. If you are used to a phone running a windows OS, a Blackberry or a Nokia then it feels just so much more advanced in someways.
However iPhone compared to say an htc Hero is like comparing a top of the range BMW with a basic entry level Ford. Yes they both do a lot of the same things but with Android its not quite as polished.
I don't know what its like in the US but in the UK and France Android handset cost a lot less than iPhone. If you are getting calendar sync and a good email system then lots of people will go for Android if they have never had these sort of things on a phone and don't want to pay the iPhone rates.
Top of the range does not = best seller.
Alex