Most likely big name games that would appeal to their crowds in their regions. Some of the best games from Sony and Nintendo make it to this side of the world long after their release in Japan and/or Europe or don't make it at all. Look how we just got Yakuza 3 a couple months back,after Yakuza 4 was released in Japan. Back in the day, when the Dreamcast first came out, I bought a Japanese model because the US market didn't have the variety of games Japan had and I bought a lot of imported games (Sonic Adventure, Sega Rally). Now, I'm not disagreeing with you about putting emphasis on E3. I'm just saying that MS has to put more effort into it than Sony and Nintendo, because this is their home base and strongest market.
Your 3rd paragraph - you are assuming that what has been leaked is all that Sony has in store. And by your thinking, they have nothing at all left to surprise us with it. If your assumption is indeed true, then I agree with you.