Not quite sure what you're on about. Your "compromise everything else" argument might hold true if we were talking about 2008's MacBook Air, but we're not. Bear in mind the 2011 Air out-performs the 2010 MacBook Pro. It's no slouch. And most people don't even need 8GB RAM really (though obviously it's good for future-proofing). My 2006 MBP tops out at 3GB, and I'm just starting to suffer performance issues.
Notice I listed all the ways the Air is better than the Pro in my post above-- might want to reread that
And to the OP: I would argue that even the higher resolution alone is reason enough to get the Air. You're getting the resolution of the 15" Pro with the form factor of the Air, meaning even if you get the high-end Air, you're still saving $200 over the baseline 15" Pro.