I recently took my road bike to the local bike shop for a tune up. I asked them to just replace any parts that needed to be replaced. The tune up was a birthday present, so I wasn't too worried about cost. I knew the brake pads and bar tape needed to be replaced, and I figured the chain needed to be replaced as well. I got the bike used as a Christmas present, and since then have logged well over 3,000 miles on it. I have never replaced the chain. I've heard that the chain should be replaced every 1,000-2,000 miles. However, the bike shop did not replace the chain. When I picked it up, the mechanic was not there. I figured they didn't replace it because it didn't need to be replaced. Now I'm wondering if I was wrong. Should they have replaced the chain?

Shifting is smooth, and I don't have any problems with my derailleur, cassette, or chain while I'm riding. I've heard that some people just replace everything at once (cassette, derailleurs, chain). Should I take the bike to another shop and get the chain replaced? Or, if I'm not having any issues, just leave it be for now? I don't mind getting everything replaced at once in a few months... I'm willing to shell out the money. I'm just wondering which approach is better. Or if I even need to really worry about this at all.

Just for reference... I'm new to cycling. My bike is a Trek 2.1 WSD. I ride 120-180mpw right now, but in the winter it's less. I've been riding for 6 months now. I appreciate any help... thanks so much!