I remeber something about Apple switching from a replaceable (though still proprietary) battery in the iPod to one that's soldered-in, rendering it non-replaceable. Is the MBA in danger of falling into the same disposeable paradigm?
The extra short answer is, no.
The MBA's battery is not actually soldered to the logic board. It connects with a small cable and plug. When you take one in to have the battery replaced at a genius bar (if thats the option you go for when it's new battery time) they'll take off the bottom case, unplug the old battery, plug in a new one, and give your machine back to you.
With iPods on the other hand. Genius bars are not equipped to dismantle iPods on the spot. So they replace it with a "remanufactured" one. Yours, in turn, gets sent back to be "remanufactured" (i.e. have its battery, case and any parts that aren't up to snuff, replaced) itself.
So while the batteries in the two products are equally out of sight of their users, the process for getting to and replacing them is very different.