How different are SW outboards?

[Jeffonc]

I've been seeing lots of coastal boats on trailers in traffic recently and found myself wondering how much difference there really is between the outboards labeled "Saltwater" and the ones not specifically labeled for salt. More/Different annodes? Different gaskets? Different metals? Different lubes? Or just different marketing?

Figured somebody out here would know...

(might be daydreaming about a flats boat, but don't tell the kayak crowd - it could lead to a shunning)