Thanks for the information. The sales figure is impressive but it's for a book. I'd expect app sales to be less than a book publisher's because users bought the kindle mainly for the ability to consume content, not apps.
OTOH, people are bound to have their Kindles with them all the time, because they're lighter and less expensive than an iPad, say. And there are times when people just want to kill time, not concentrate on reading. So, if it's a game you have, you might want to consider that. Plus, the rumored KindlePad, which will do more than just read books (I know bringing this up seems to contradict my first point, but still. People have their libraries in K format, so they'd be more likely to also buy that Pad.)