Interesting, I didn't know that. Why would it have high copper content though? I thought the main thing that killed brake fluid was getting water in it, and getting burned. Does some chemical reaction cause copper to form?
I think subaru says to change the brake fluid every year, or something. I usually flush mine once a year, it's easy, and helps keep rust and crap out of the system.
I recently had a rear caliper on my legacy partially seize up, it was just full of rust and crap. Cleaned it out and it's working fine now! A good testament that flushing your brakes does help the system live longer.