Aluminum immediately oxidizes and that layer of oxidation provides a protective barrier to further oxidation. Steel just keeps oxidizing.

Some of the newer de-icing sprays that are put down will oxidize aluminum faster.

I don't wash my aluminum frame all winter... no problem.

Fenders with a large mud flap keep your ride mostly clean.
Run full housing to your gears, they'll be fine almost all of the time... run single speed if you want.
The big problem around here is the freehub grease gets water in it and freezes. Flush it with a lighter oil.