Erm, the MacBook Air customer isn't getting it instead of a MacBook Pro. They may well be the same customer, but that would be to supplement the Pro not replace it.
I have a MacBook Pro 15". It's the 2007 one with a 2.4GHz Core2Duo, 4GB RAM, 500GB 7200RPM HDD, 1440*900 Matte screen.
The 3 years AppleCare expired this summer.
I very nearly went and bought the current one to replace it (2.6GHz i7 [though now there's 2.8GHz], 8GB RAM, 1680*1050 Matte screen), but decided to keep my current one going until the 2011 Sandy Bridge one's come out. Touch-wood it'll survive until then, it's had two keyboards/mice & two batteries & a new superdrive & a new logic board in it's life.
I'm considering a MacBook Air. 11", 1.6GHz Core2Duo, 4GB RAM, 128GB Flash. This is as-well as my current (and future) 15" MacBook Pro.
The MacBook Air does not replace a MacBook Pro. A 13" MacBook Air could possibly replace a 13" MacBook, but there is no way that the Air can replace a Pro.
From
http://www.anandtech.com/show/3991/apples-2010-macbook-air-11-13inch-reviewed:
"For me, Id have to own the 11-inch [MacBook Air], plus a 15-inch MacBook Pro plus my desktop. Thats three machines, plus a smartphone and Id be set. Id carry the 11-inch on most business trips, the 15-inch for big shows that Id have to cover and any heavier work Id do at home on the desktop. I dont mind the setup, its just a costly setup to have."
With regards to the idea of using Apple's Flash Stick instead of 2.5" SSDs..... as-long as they are after-market replaceable I'm OK with it. If you're stuck with the performance and capacity of the one it shipped with then no I'm not OK with it. I wouldn't get Apple's SSD in a MacBook Pro, I'd do it myself with an OWC one. Far better performance.