Actually I very much doubt the retina model would be as fast as current model.
Current MBA is using HD5000 and there is no any other integrated gpu chip which would archieve the same performance on retina as HD5000 archieves on 1440x900. And obviously there is no way non-integrated gpu will fit in MBA.
You make a good point. My argument was that the new one wouldn't have any performance benefit, so I didn't take the time to fully flesh out the argument. I'd be interested to see what Apple is planning for A-series notebooks, as it seems like they are focusing on graphics performance with A-series chips. Also, broadwell should give a significant GPU boost, so it isn't 100% a fact that performance will be worse than the hd5000 model.
Matt