|Check out the larger version here.|
|This shows how few paid apps are sold; larger version here.|
Here's reality: Some 96% of Android apps sell less than 1,000 units, and most of those are less than 100 units. If you are a developer, you can see you're unlikely to make any money from your Android app.
While Google has been working on improvements to the Android Market, and selling lots of Android devices, you can't count on that to lift your app revenue to the point of profitability. So why do an Android app at all? Perhaps you can cross-sell a number of other apps, or hope to monetize your app through advertising (but that means getting lots of downloads). Maybe you have other products your app can help you sell... or maybe you just want to try out some design ideas when there's no restrictions on what sort of app you can offer.
I can't emphasize enough the importance of proper business planning before you spend any time developing an app, either for Android or iOS. Really, while the situation is certainly better for an iOS app, it's not all that dissimilar. Most iOS apps sell less than 1,000 units, too. That's not a great return unless you only spent an hour or two putting your app together, which seems unlikely.
A successful app is going to be a lucky break, and it's going to have to be very well executed, too. Regular updated content and solid marketing are going to help, but there's no magic potion that will make your app a hit.