Seriously, changing your shirt? This isn't Barbara Striesand. Did Joe Strummer change his shirt?
no, but off the top of my head i can remember that trent reznor and thom york have. i know, i know, they don't meet with your hipsterific approval ("sell-outs", "pussies", etc), but that isn't the issue at hand - the question is whether an encore can serve the purpose of allowing an artist to get out of their sweaty clothing. having seen both these bands previously on the tour, i can assure you these weren't wardrobe changes - they were artists who had sweated their asses off in an over-heated venue, and appreciated the opportunity that the 5-minute encore afforded them to get in to a dry shirt. i've seen other musicians to it as well. i'm not saying it's the main function of an encore, it's just one of the reasons an artist might appreciate a short break.
anyhoo, this isn't about "proof", and neither of us is going to change the other's mind. i'm a nancy, and you're self-centered - so let's get back to talking about how great the TCV show was