the "slowness" of java comes from its native interface intermediate layer. basically speaking even if the java code itself is fairly fast (especially if it uses multiple threads) the bottle neck will be the interactions with the native libraries. for example every call from java to opengl library has to go through this native interface layer which slows down every individual call. it's not noticeable if you make 5-10 calls, however, 100-1000 calls already make a significant slowdown. now if you are making a game, how many opengl function calls are you going to make to do your rendering?

I agree that for OUYA this may not be a major problem especially if you are making a small game, because the hardware is fairly powerful and is in fact designed specifically for games. however, for the mobile devices and performance intensive games this is a very important issue. many android games are now made using the NDK instead of java.