The pitting is caused by leaving dead bugs on them. Never leave dead bugs on your bike. I always wiped my motorcycles down with pro shine before they go to bed. I have a 98 with the original clear coat on the front forks. No pitting, even where rocks have removed clear coat over the aluminum.
Good advise...I always wipe mine down with a wet micro fiber towel and then dry them off after I'm done riding for the day. It takes a couple of minutes and no pitting at all.