You have that. It's called the Android market. "Well, just let the market decide" is a naive/overly simplistic approach. There is an issue of people being able to find the apps their looking for and it's not easy to solve. The more rubbish apps you have the harder it is for people to find things they like. Eventually
your app store gets the reputation of being filled with crap.
The market does come into play though. For the app stores. Last I heard, your Android app making 50% of what your Apple one does is a realistic expectation.