Well, Sony is capturing both and it's working!
They have reduced the lead between 360 and PS3. That way they wont abandon hardcore or casual gamers like Nintendo and MS have.
MS is focusing on Kinect and forgetting about others.
Nintendo had focused on Casual in the Wii, so even 3rd parties Had abandoned them.
Microsoft have forgotten about the core? Halo 4, Gears of War 3, Forza 4, Halo Anniversary, and the countless core multi-plats disagree with you.
Microsoft is focusing however on the casual more than the core at the moment but that's not really a big deal. Like the OP said they already have the core now their trying to expand out their fanbase.