Cave and MS have had a pretty successful relationship for some time now. I don't think bribes are necessary, although they might have waved a few fees
I'm sure some flavor of this game will eventually make it to iOS where it will sell literally 1000x as many copies. For now they are trying to make Windows Phone actually sell, which doesn't seem to be working, which is kind of sad since its actually pretty cool. While I prefer iOS and the iPhone, and probably always will, in order for competition to push things forward there needs to be a true competitor, not just a knock-off. Android OS and the phones still feel like scatterbrained, low rent trash by comparison. There is no question that Windows and Mac OS both improved MASSIVELY in the last decade and neither would have done so if they were the only game in town.
Regarding Cave games on phones; ESPGaluda II is one of
maybe 10 phone games I've actually found entertaining enough to actually play for more than 30 seconds. Others: Robot Unicorn Attack (both), Game Dev Story, FIFA 2011, and most recently, ZiGGURAT.