My perspective, as the owner of a painted non-stainless-steel bike (True Temper OX air-hardened steel) with S&S couplers that I travel with quite a lot (10 round trip flights in the past three years):

Judging by the writeup above, the purpose of the stainless steel in this particular case is for cosmetics and convenience. When I pack my steel Rodriguez fixie for airline travel, after I uncouple the frame (which takes less than a minute), I need to spend the next half hour wrapping each frame tube and fork blade in the velcro-backed neoprene packing material. If you get a coupled frame built at R+E Cycles in Seattle, they include the custom-cut packing material as well as an instruction session in packing the bike. Wrapping the tubes in this material is the most time-consuming part of packng, and if you don't do it, your frame is guaranteed to have all sorts of scratches by the end of the trip. Jeez, it'll even have scratches if you just close the travel box on it!

So if you build the frame out of stainless steel, you can avoid having to wrap the tubes, which will save you a good half hour, so you can probably pack the bike in about fifteen minutes. And even if the tubes get scratched up, you can just buff out the scratches. Cosmetics and convenience.

That said, back in the 70's, the Swedish bicycle company Crescent built a stainless steel model (no couplers, though - I don't think they'd been invented yet). I knew a guy who bought one. It was unpainted when I first saw it. I saw it again a few months later, and it was still unpainted, but it had all sorts of dents in the tubing. The material was pretty soft.

Luis