The latest version of Android, dubbed Ice Cream Sandwich, is running on fewer than . (About 64 percent of Android devices are running Gingerbread, which was released at the end of 2010 and supplanted--in theory--by Honeycomb, before Ice Cream Sandwich's release.)

Reports peg adoption of Apple's latest iOS release, iOS 5.1, at nearly .

Thus, Android phones are the printers, and developers who want to make apps must build the ink. Ever felt lost in your local office supply store as you try to find the right black ink for your printer? There are oodles of models and sizes--even within brands. Developers making apps for Android, in effect, need to make ink that works with every printer.

On the iOS side, things are considerably simpler. To push the analogy to its limits, successive iOS devices might print faster or higher quality images, but they still take the same ink.