Stainless steel rads can't be all that bad according to this graph from Lytron:
These heat exchangers are identical except for the tubing material. Perhaps they use some special alloy that "doesn't suck."
And shouldn't we be talking about corrosion between chromium oxide and copper?
Update: Lytron uses 316L stainless steel that is "mechanically expanded into the copper fins for an intimate thermal connection."