From what I've seen and read, it's about the same size as the normal one (maybe even exactly the same). It just appears larger in photos because of the reduced space around it.
Edit: Apple likes to keep them the same across all models (with the exception of the 11-inch Air, due to size), since it's consistent for users and also means the lineup can share the same part! I'd be surprised if the new 13-inch MacBook Pro with Retina display has a different trackpad to the one in the new MacBook.