I don't get it. Help me understand.
The extra money goes into the SSD, which for some reason you omitted from your comparison. It's fast and reliable.
The rest of your comparison isn't really relevant, since the base MBA is a lot cheaper than your MBP. But still:
I don't have your need for speed. If you're a graphics professional you probably need all those applications, but as a software guy I've learned one lesson: multitasking is bad for you (me).
I do research in genetics (bioinformatics) so I'd count myself as a power user. But I've never had a need for more than the MBA offers. The simulations run on a cluster anyway. As for storage capacity: a base install of OS and Software takes 20GB at most, and 44GB should be enough, at least on the road. I can only think of professional photographers and these people that obsess about the size of their movie library to need more than that. Personally, I never watch a movie twice, so taking two or three on a trip and then deleting them works fine.
Which brings us to the advantages: If you spend every third week at a conference, you'll start to notice the 2lb rather quickly. How many times did I take my powerbook with me only to regret it when I had to carry it for a whole day? Other times I thought I learned and didn't take it, only to then regret that decision.
Summa sumarum: to each his own.