I think there are two demographics. iPhone users already are used to buying music and have an iTunes account. It's a natural progession to buy apps. Android

I think there are two demographics. iPhone users already are used to buying music and have an iTunes account. It's a natural progession to buy apps. Android many probably hate iTunes and used p2p; Other issues are... - Google Checkout - Apps not being sold internationally - As noted above a messy marketplace; yet Google's focus is the web not apps.