I'm pretty sure that is an optical illusion and the right rear is not up in the air in that picture if that is what you are referring to!! lol...
When I first saw that picture, I immediately went to the high res version of it to make sure.
http://imgur.com/a/oK198#24
If the car was cornering flatter and the inside rear was in the track more, I'd be carrying even more speed and still putting a tremendous amount of pressure on the outside wheel. The wheel is still going to flex until the tire breaks traction and begins to slide.
Besides, Ron likes the inside rear to roll up some to let it release from the track to help the car corner. He is more concerned about the front not rolling as much moreso than the rear.