I developed my first iOS app about a year and a half ago, and it has seen over 2,500 downloads (it's a free app, and pretty useful, albeit only for a certain portion of people living in St. Louis, MO).
I developed my second iOS app (a companion to a news aggregation website that's existed since 2009) in April 2011, and in the first month alone, it was purchased ($0.99) over 300 times. In the months that followed, the app has consistently sold over 50 copies, sometimes more than 100, without—literally—any marketing on my part. Just an occasional plug on Twitter or at a conference. That's it.
I then decided to finally take the plunge and try my hand at redeveloping the app for Android (my first Java/Android project), and worked very hard to make the app run as good, and sometimes even better on Android phones (anything running 2.2+...).
Translation: Why I won't develop for Android first (no matter the marketshare).
The first month of sales have been more than disappointing; after 8 sales on the first day—most to friends who I specifically asked to download the app and test it*—the app has sold maybe one or no copies each day since, and all in the U.S. (The app has four five star reviews, the market page, icon, etc. are all very good quality—I spent a lot of time on the text, design, icon, etc., even forming everything to Android Market/platform standards instead of reusing iOS resources).