So going forward, the Pro will offer vs. the Air:
- Retina display
- Quad core processor
- Discrete graphics
- Twice as much RAM capacity
- HDMI
- SDXC card slot
- Audio line out
- Dual microphones
This assumes of course, that the forthcoming 13" Retina Pro has all of these same features that the 15" one does (I think it is a pretty safe bet, though I could also see the HDMI port being omitted from the 13").
Formerly the Pro offered vs. the Air:
- Faster processor
- Discrete graphics
- Twice as much RAM capacity
- SDXC card slot
- Optical drive
- Firewire port
- Ethernet port
- Audio line out
- Kennsington lock slot
I may have missed some minor items on those lists.
I expect the legacy Pro models will soon disappear, perhaps with the introduction of the new Retina 13" Pro, or perhaps after the possible introduction of a future 15" Air.
I also think that, eventually, the Airs will get Retina displays as well. I wonder what resolution a 11" retina display would have? Perhaps 2048x1280.