Idk, maybe the retina screen?13" Retina MBP doesn't make sense.
How would it differ from the 13" MBA?
The 13" rMBP wouldn't have an optical drive, so the only differentiating factor would have to be the CPU and GPU. So far the 13" MBPs had the same graphics as MBAs.
The CPU? This one gets just under 8000, while the 13" MBA gets 7000.
So tell me, what would set the 13" Retina MBP apart from 13" MBA?