It may have to do with the metals that are used - If aluminum touches steel and you put it in salt water - you've basically made a battery and the corrosion happens pretty fast. I know if I'm kayaking in salt water, there are somethings that corrode within one or two trips - the zipper on my pfd, etc.

It may be the other bikes that you use in salt in winter either have different metals, painted drop outs or you're more meticulous cleaning the salt off. I don't know if the drop outs on that mountain bike fork are magnesium, steel or aluminum. Probably the shaft of your quick release is steel - the ends of the quick release are probably aluminum.