The key is the content and the support. Android is gaining and is pretty much very similar with iPhone. But, iPhone has a full support from single company, Apple. Where else, Android has multiple support, such as, HTC/Motorola for the hardwares and Google Android as OS.
Then we can talk about contents. Apple provide all music, apps, and iOS update. Where else, Android, OS update is done by Google. Then all the Android owners have to wait for their update through HTC/Motorola which is not immediate since they have tweaked or personalized the Android OS.
Apple makes thing easier. When Android has this kind of support and contents, Android will sell like peanuts.