While what Ed said about the AppStore is true, it is becoming oversaturated, because Apple can't keep up:
Apple Insider
Moreover, the design of the iTunes store itself is not very conducive to searching and finding the applications you need out of the 95% of the trash.
I am sure google is much aware of this and I hope Android Market will find a way to avoid the mess that the AppStore has become. If they do, developers writing good apps for Android would have higher financial returns in the long run.