The number of Android devices may be growing like a weed, but when it comes to the ecoystem, not all is well.

Google’s Android app store, Android Market, isn’t nearly as vibrant. Whether due to stingy users, a poor experience or a combination of factors, the risk is clear: if developers treat it like the iPhone’s ugly cousin, Android may have tougher times ahead.

Already, there’s reason Google should be very concerned. That’s because the App Store is surging…

Last week, Apple announced the 15th billion download of an app from the App Store.

But Apple isn’t just winning the volume game. According to an analysis by Piper Jaffray analyst Gene Munster, iOS device owners are going to download 61% more apps this year than they did in 2010.

And, following a decline in 2010, the average selling price of an app is up 14% this year, to $1.44/app, due in part to the proliferation of apps designed for the iPad.

As Fortune’s Philip Elmer-Dewitt notes, the App Store makes up a small fraction of Apple’s total revenue, “but without the App Store, Apple wouldn’t be able to sell iPhones and iPads as fast as it can make them“.

It’s a vicious cycle, and the more compelling apps that are developed for iOS, the more we can expect consumers to buy iOS devices. And the more consumers buy iOS devices, the more we can expect developers to focus their development efforts on them.

Right now, Google isn’t having any trouble growing Android’s market share, and there will always be a place in the mobile market for iOS alternatives.

Yet as mobile consumers get more and more sophisticated, and the market for mobile applications matures, one has to question just how much further Google can go before it has to decide whether Android will remain an iOS alternative or become a mobile second class citizen.