If Apple has a slick new MacBook Pro lineup ready next week, Steve is going to wait until the 11th so he can wow the crowd with it. That's all there is to it. If it's just a so so update, he wouldn't want to brag about it so it might happen before the event, or quietly during the event.
I don't think there will be hardly any discussion of iPhone at WWDC. Rather, there will be a special event for that later in the month.
IMO, the WWDC keynote is going to be about Leopard, mostly. There might be a new piece of hardware introduced at the keynote, but I'm not counting on it. As I've already said in earlier posts, my bet would be on a 13" MBP but that's just because it's what I want to see, not because I think I really know.