My thoughts about the Air (though I don't really know) was that they sort of put it out there & let Moore's Law get to work.
It's not a very practical product as is.
I imagine the attractiveness of a netbok to Apple is that it is an addition. You can have a laptop or desktop (probably not both) & a netbook & an iphone.
If it is a non cannibalising category, then it's right up Apple's game. They know & love small. It's another opportunity to brag about OSX as Windows isn't right for these. Most importantly, they know & love out-of-the-box.
There's a real market for these. It's certainly not the giant hardware guys that created it. They're supplying happily enough, but it came out of the margins. Microsoft sure isn't pushing it, these are a nightmare for them. Linux isn't working out. Who's left?
Cheap is part of the job description here. Cheap, small & out of the box. Apples is very good at 2 out of those 3. It's also another in for selling full Macs.