DuffDuff... what an insightful post.
Why the extra content for the Wii versions? It could be a myriad of reasons.
1. It costs less to produce
2. It caters to the Wii demographics, which are social players who enjoy local multiplayer titles. (Just look at the sales of titles that meet that criteria, Sonic-Mario-Olympics, Super Smash Bros, Carnival Games, Mario Party)
3. The Wii is the console to most likely be part of a multiple console household, so potentially a fan could buy two versions of the same game.
I honestly don't know what was considered in these decisions but as a Wii only owner it makes me smile as those two titles you mentioned are titles I intend to pick up (Star Wars & James Bond) and I get two features that sound really cool to me.
Is the X360 holding the PS3 back?
That's an interesting thought. If developers are assembling the same team to produce games for both then yes, because that extra space the Blu ray disc brings in isn't being fully utilized, That extra space gives game developers space to put more levels, more quests, and more content. To pack a game with almost five times as much content is unheard of in a cross console title, and would certainly be a selling feature in favor of Sony if developers opted to do so. How could anyone justify to buy a game if another console had the same title with five times as many levels? However packing that much more content probably increases dev costs significantly.
Incidentally anyone who remarks that X360 DVD drive can pack more content than the Wii Optical drive, needs to check the specs. They pack the same amount. Dual sided or not.