Say what you will about platforms, but in 2009, Apple's App Store absolutely pwnd the paid mobile app space - selling 99.4 per cent of the $US4.2 billion market singlehandedly, according to ars technica.
This data is based upon research by Gartner, who claims that, should sale trends continue, Apple could retain two-thirds of the paid mobile app market into 2010 (amidst growing competition from Android, Palm, RIM, etc). Of course, if Apple releases an app-wielding tablet, marketshare could error greatly in their favour again.
(Note: there's some discrepancy in these numbers, as Engadget corrects ars' number crunching from 99.4 per cent to 97.5 per cent. Whatever, either way, it's enough of the market to mean every other retailer was moot in 2009.)