It may sound odd, but last year I had a 13" MBP (4.5 lbs), and its weight really bothered me. I actually swapped it for a mac mini that I carried to and from work each day, hooking it up to a monitor, keyboard and mouse at each place just because it was a bit lighter.
The only I'd want an air over a pro is the weight. As far as the X220 is concerned, weight would be my number #2 complaint after the OS. The lack of an Apple-level quality trackpad might be #3. The hundred bucks does matter, but honestly when you consider how many hours you, or at least I, spend on a computer, the price is almost negligible compared to improvements in user-experience or efficiency.
The only I'd want an air over a pro is the weight. As far as the X220 is concerned, weight would be my number #2 complaint after the OS. The lack of an Apple-level quality trackpad might be #3. The hundred bucks does matter, but honestly when you consider how many hours you, or at least I, spend on a computer, the price is almost negligible compared to improvements in user-experience or efficiency.