850 miles on a chain doesn't seem that bad to me, especially if you're a big guy like me. As cheap as chains are I just replace them every 1000 miles or so, I stretched out a shimano 9sp hg-93 in 700 miles the stock chain had less than 400 (some kind of sram chain). I know the bike I had when I was a kid had 10-20k miles on it, never replaced a chain or cassette, never knew i was supposed to and it always worked great.
I think it's cool how you guys are so quick to bash the LBS guys. Do you really think the guys went in the back room and said "hey, let's screw this guy and sell him a chain he doesn't need"? Come-on that's crazy.