I suspect they use steel because it is much cheaper to etch. The usual etching solution is Ferric Chloride, which has some weird chemical properties, in that as it etches steel it just changes the valency of the iron atoms and keeps on etching!! Because you are adding more and more Iron, of course eventually the solution becomes exhausted, but you can recover it by adding hydrochloric acid. You end up producing more and more ferric chloride! This has some value, it is used in treating sewage for example, so the excess can earn the etcher a little bit of money. If you etch brass, copper, bronze, when the etchant is exhausted it costs a great deal to dispose of properly, because it is now contaminated with copper, tin and other metals.
Stainless is not a very nice material for modellers though. It is hard, cracks easily, you can't solder it, if you do bend it it is impossible to straighten again. But it doesn't tarnish, so it looks nice in the packaging for longer....
Exactly, Tim. This is something we do daily in my company. I should add that etching stainless steel does not produce a very "clean" etch, at least at microscopic level, because of the chromium crystals it contains.
Not sure if the Flightpath set is stainless though (altough most likely). I did manage to soft-solder my reinforcing strips on the outside.
@ Max: thank you for chiming in. I hope this is going to be straightforward, well sort of ...