I intended to buy a MBP 13", but now I think I'll go with the Air.
Apart from a small subset of people who need CPU speed over all else (but don't go for a 15" to get the discrete GPU), the only real selling points of the 13" MBP now seem to be the extra connectivity, the optical drive and the possibility of 500 or 750 GB of internal storage without a second mortgage.
No Ethernet and/or Firewire will be the deal-braker for some, especially if they also use an external monitor (only the one Thunderbolt port, which doubles as the external monitor port, and those Apple dongles don't look like they daisy-chain). That's not such an issue on the Retina Pro with two TB ports and HDMI as an alternative monitor out.
Of course, if you spring for an Apple Thunderbolt Display, that's your connectivity sorted out.