Steve Jobs thought about putting iTunes on Android much like Apple did for Microsoft's Windows platform, but the move didn't make sense. Why? Jobs didn't want to "make Android users happy."
Walter Isaacson's biography of Steve Jobs contains a lot of Android references. Jobs blew up when Google decided to launch Android and panned the search giant every time he could. The Apple-Android duel has led to a bevy of lawsuits. Ultimately, Jobs viewed Android as a "stolen product."
Jobs felt the same way about Microsoft Windows in some respects, but hell can freeze over when hardware sales are at stake.
In the biography, Isaacson quotes Jobs:
"We thought about whether we should do a music client for Android. We put iTunes on Windows in order to sell more iPods. But I don't see an advantage of putting our own music app on Android, except to make Android users happy. And I don't want to make Android users happy."
Jobs' calculus works out based on real dollars. Apple makes out nicely on iTunes, but the service's real benefit is to sell hardware---lots of it.