Are you regularly (every 200 miles or so) degreasing and lubing the chain? If not, coupled with riding in rain/muck of the PNW, I could see maybe blowing through chains every 1000 miles or so - MAYBE.
Other than that, the specs on your bike seem like it should be fairly reliable.
What other repairs besides the chain and cassette got you to the $500-600 mark within a year?
I vote finding a new bicycle shop.