"All of that being said, I don't really view the 13-inch rMBP as an alternative to the 15, but rather a step up from the MacBook Air. The MBA may be lighter, but Apple definitely blurred the line between the MBA and MBP with the 13-inch Retina. Performance is very similar between the two machines, but the rMBP's display is worlds better. For any power user, I don't know that I'd recommend the 13-inch MacBook Air over the 13-inch Retina MacBook Pro. It really is the best of both worlds."
From Anandtech