We don't even know, and Sony, Nintendo and Apple don't, either, whether 3DS will repeat DS' success or whether iGame (or whatever) will succeed or not, so it's a little bit early to predict Sony's retreat. With this attitude Apple shouldn't even try. If they keep costs under control, even a 20% share of next gen should be enough for not giving up, Nintendo didn't give up on home consoles market when GC dropped under 20%.
If nothing else, Apple's entry should make things even more unpredictable, whoever retreats without fighting just leaves it free room, but the more the competitors really willing to fight are, the smaller the winner's share willl be (and the winner could even be the outsider, Apple, as far as we know now).