I am running Pandora on both Android and IOS device simultaneously. Pandora is playing almost twice as many ads on Android. I don't have historical data on Android ads but I suspect Pandora is tweaking their device related algorithm to retain more IOS users for now. Or, they may be balancing their revenue goals by increasing number of ads on Android while decreasing ads on IOS.
I found the divergence interesting given that iRadio is running less frequent ads and free users are liking that aspect of Apple's service.