Define "mobile."
I have a 13" Macbook Air (2011). I rarely take it out of the house. I take it out of the house so infrequently that weight is a non-issue for me when traveling.
What *is* important to me, however, is "lap weight." Call me crazy, but I actually use this laptop on my lap. Most of the time, in fact. I work out of my home and move from room to room. Most of the time, I use it on my lap. I may very well come to regret my usage habits at some point, if I start to develop back problems from using my laptop 10+ hours a day on the couch, bed, etc., but for now, that's how I like to use it. I honestly can't imagine forcing myself to sit at a desk 8+ hours a day. We have a perfectly fine home office (my wife likes to work out of it on days that she works from home). For me, even when it's available, I have little desire to work out of that room.
Also, I partially attribute the Macbook Pro (non-retina)'s added weight/size as being largely wasted on that DVD drive that I have absolutely no use for. At least with the Pro Retina, they got rid of that and saved some size/weight as a result.
I will admit that if the Pro Retina was available at the time I got my Air, it would have probably been the one I wanted, primarily for the added screen size/resolution, just as I opted for the 13" Air over the 11" in order to get more resolution. The other "Pro" features (e.g., faster CPU) are currently unnecessary for my needs. I'm a programmer, but focus these days on SQL and development that is conducted on a remote machine, so I'm rarely taxing my Air's CPU. I do want to get into iOS development, but I have trouble believing that the 13" Air (2011)'s CPU would not be more than sufficient for that.
Why are we having this discussion in a Mac Mini forum, anyway?