According to this piece in Electronista, a recent AdMob study estimates Android Market's paid app market is only worth $5 million, and even high-profile, highly rated Android titles generate "much lower" revenue than iPhone equivalents.

Despite having one sustained top-selling $5 game (Retro Defense), a consistent fifth place seller (Battle for Mars) and being highlighted by Google, the company's daily average revenue was just $62.39 for all its apps combined.

In comparison, an iPhone app with a fifth place position in the App Store is predicted to earn about $3,500 per day, or more than what the same Android title would generate in 56 days.

Electronista blames the poor revenue on Google's approach to marketing paid apps on Android Market. The company defaults to showing free apps first and forces users to enable viewing paid apps themselves. Apps are also limited to a short 325-character description and can't even come with screenshots.

Finally, Google Checkout is the only choice to buy, and failed  downloads are a significant problem on Android Market.