I think there's two effects here - one is that on IGS communication between players is usually just "Hi" and "Thanks for the game". These people just want to play games, and let's be honest even if they thought you were a sandbagger/overrated/go-playing cat you would have no idea what the other person really thinks because it's never shared. KGS has a decent amount of these people as well, but I'll agree IGS has a much larger percentage. The second thing is that those who chat on KGS are much more likely to be those who play fewer games, and thus worry about the results of specific games, try to find justifications for outcomes of single games, etc. (If you play 20 games/day rapidfire, it's hard to get stressed out about why you lost game #4 of 20...if you play 20 games/year it's easy to dwell on all of them). The result is that if you are reading the chat, you are more likely to see the thoughts of a disproportionately high number of people worried about sandbaggers, escapers, cheaters, and curiously adept felines.

I like yahoo's Go server. Kind of cutey and weirdy.