Welcome to the shandy world of emulators. If you take a look on the Android market, you're bound to find a load of game emulators ranging from the SNES to the Playstation. You can understand why they exist, Angry Birds has only got so much longevity. As the release of the Xperia Play has shown, people want to play games, real, full games on their phones, and of course people LOVE retro, if you can play Super Mario World, Turtles in Time or F-Zero on your Android phone/tablet you are instantly cool.
The emulators themselves are legal too, in fact when Sony tried to take out a Playstation emulator, the found they had no legal grounds to do so, in the end they managed to pull PSX4Droid off the Android market by claiming copyright infringement (due to the PSX prefix.) What is illegal though is the ROMS, but ROMS aren't floating around on the Android market. So despite it being well known that emulators are used to illegally play awesome retro games, they can't technically be touched.
But despite this, Google are clamping down on emulators big style. Emulator superstar Yong Zhang the creator of the popular apps such as Nesoid, Snesoid, N64oid, and Gameboid has had his Android developers account suspended and all his apps deleted.
But why? no one knows. Speculation is that Sony, Nintendo or Playstation put pressure on Google. It'll all come out eventually. But banning emulators is fruitless, they're always going to be around. There must be a better way to combat the problem, one that keeps retro gamers and Nintendo's attorney happy. In the meantime Yong has moved the apps to third party Android store, Slide Me.