Winning big games is only party of it, IMO any of the bigger teams can beat eachother on any given day regardless of form. The decider for me is consistency, something the ''smaller'' teams struggle with because of depth amongst other reasons.
Chelsea probably have the most depth in the whole league, more than the other teams of the big 4. Teams like Man City, Blackburn, Newcastle and Everton don't have the same depth; that's what I think will make the difference.
The big Chelsea killer though will be the AFC. I think we can hold down the midfield pretty well in the absence of Essien and Mikel but who the hell is going to score goals? Sheva? HAHAHA, Drogba (and Kalou even) will be sorely missed up front because quite frankly I don't think Sheva or Pizarro can carry the load.