What's the point of the 13" Air versus the 13" Retina Pro

In terms of size and weight, they are very close and if the rumours are true they will be even closer. The lowest end Air costs $300 less than the lowest end Pro but saving up another $300 can't be too bad when you are already spending $1000+ on a laptop. For the $300 you get a faster processor, double the RAM, double the storage, an extra thunderbolt port, an hdmi port, and of course that super high resolution retina display. Certainly worth the $300.

Help me understand!