I completely agree with the poster who brought up margins. Apple makes more on average on a per device basis than Google. However....
As any psychologist will tell you - perception is reality. Despite the number of purported Android devices, if all everyone ever sees are iPhones then people will continue to believe that Apple is outselling the competition.
The other issue one poster touched on was Apple as a status brand. People don't aspire to own a Droid

- people want to own iPhones.

It sort of reminds me of the Fortune interview with John Sculley. When he got to Apple from Pepsi he relayed market research to Steve Jobs about how they'd learned that people with Coke would bring out the can and pour it in front of friends when they asked for a drink where people with Pepsi would pour it in the kitchen and bring out only the glass with the Pepsi in it to their friends leaving the can or bottle in the kitchen.