If Google's goal is getting emulators off the market, they're doing a pretty poor job of it:

https://market.android.com/search?q=emulator&so=1&c=...

Great point, then maybe avree (above) is correct and the code was indeed stolen.

That's a fair argument regarding PSX4Droid, but I doubt that's the case with this group of emulators. Sony doesn't have any relationship with the SNES or the Genesis, so with the exception of maybe a few ported games, it's doubtful they'll be selling that IP on their own store. In fact, the controller on the Xperia Play would make those emulators a pretty compelling reason to buy it.

I'd wager this was related to either ROM distribution or violating the license on the emulator code.

I doubt this is about "keeping Sony happy" specifically.

It might be that Sony is the entity that raised the infringements to their attention, if the reports of GPL infringement and other "non-commercial use" licensing issues are correct.

Why would Sony be defending GPLed code? Possibly following "the enemy of my enemy can at least be used to inconvenience my enemy" rule. Though there is no evidence that a high profile company is behind the take-down at all - it could well be that one or more of the open source projects caught wind of their code being used in breach of their chosen license and complained to Google and that the timing of Xperia's launch is a coincidence.