As long as Sony and MS fight each other for hardcore, they can't fight properly Nintendo too for casuals. And their motion controls show it, Sony wants a more hardcore kind of it that will overlap very little with Nintendo (although it will ease 3rd party ports), MS started well with a different approach, but ruined everything with its uninspired "mii too" launch games. And on portables, PSP has its niche that doesn't affect at all DS.
But Apple won't care at all about Sony and MS and will directly attack Nintendo. Yes, it could be one of Apple's flops, but they became rarer and rarer in recent times.
About Google, well, up until now it preferred to hit mainly MS: even Android didn't damage iPhone at all, but it dealt a mighty blow to Win CE/Mobile, so it's quite likely that its entry into gaming market could either hit MS home consoles and maybe even Windows gaming or hinder MS entry into portables.
