Yes Sony will probably steal the show. They have to. I really don't mean this sarcastically: they need some vaporware, Killzone is become real they need more stuff years away to show us the potential for PS3.
Nintendo will be a no-show, but with a key-note. I would be surprised if Nintendo, in 2 hours, can out shine PS3 in 3 days.
I would cite regulation, but I know you will simply ignore it.