One of the problems with all the app stores is "app discovery" it's searchable but if it's a common keyword maybe you don't find exactly what you are looking for. I can't imagine it's much longer before apple and google begin to sell "adwords" for apps. My guess is that it would work exactly like adwords works today on the google search site. Based on rankings, downloads, and price you are willing to pay some of the results will be sponsored ads. It's pretty easy money for both Apple/Google and really helps those in the marketplace who have a great product "buy" their way to critical mass. We are retuning to "walled gardens" and closed systems, Google was smart to get into the moblie space in a big way, if they are going to maintain growth it will need to be through mobile and that will mean more than just ads on search.
I'm building a startup called ServiceVines. I live far out from civilization and like it. I get really too excited over tech, economics, and food.