Well, actually, in ST09, I got the impression they made Kirk and Spock central, with heaping helpings of Scotty because he's Simon Pegg and Uhura because she takes her clothes off with everyone else secondary.

But while Kirk, Spock, and McCoy were central, the stories I've read usually involve Shatner petitioning to take away the moments the other characters had for himself. Or that a shot would be set-up to highlight a certain actor, Shatner would pull the director aside, and when they came back, it was Shatner being focused on. Now, I'm not sure how true that is, but I did recently notice a striking difference between the earliest episodes and everything that came after. If you look at episodes like "The Man Trap," "Charlie X," and "The Naked Time," you'll see lots of scenes that focus on the other characters and shipboard life. Scenes without Shatner. But very quickly, those fade away. Now whether that's Shatner's fault or just a shift in focus by the writers or network, I don't know.