this certainly does support your theory. I was rather skeptical but those two photos are interesting, especially if your other bikes don't exhibit any of the same thing.
re pedals, always put a good layer of grease on the threads before putting them on, and you will really need to use a metal brush or something on those rusted threads (and probably the inside of the hole on the crank arm) before putting them back on. Id be rather liberal with grease anywhere you see any hint of rust where threads are involved. I guess for the crank you could put a thin layer all over that area, but then you get back to having to be careful for pants etc.

as for a dirtier chain, I cant see how you will be able to avoid this, as a physical layer of surface oil will probably be the best protection any chain on this bike will have.

getting back to not using a solvent regularly-I see a frequently oiled chain always being better for rainy conditions (or your particular one) as a layer of oil will always be moving out onto all surfaces and help keeping rust at bay. When I ride in rain, a heavier oil such as Phil Woods has been better in my experience for keeping surface rust from appearing, but as you say, the chain will always be inherently dirtier, but I guess that will be the tradeoff. Im pretty picky about keeping my chains lubed, and always do a wipedown and relube after riding in rain, which is certainly better than ignoring it which has nearly always had surface rust appear fairly soon.

good luck with that chain.