I'm not surprised at all. The mobile market is a much more compelling _user scenario_ than desktop, both in terms of the user-need and the user-interface. On mobile, the user-need can be satisfied much better with additional sensor data that aren't common in computers today. The user-interface, too, is why it's a much more compelling mobile offering than a desktop offering (collating all that information in mobile between multiple apps would be annoying, not so much with a multi-tabbed browser or multiple windows)

Besides, Google has been killing it on iOS recently.