Frequency of replacing parts

[Grog]

Salt could explain a damaged derailleur...

I am a light rider and tolerate chainstretch until it's really bad. I do around 5,000 km on a chain and middle chainring, but my cassette sometimes lasts longer because I really use all gears.

[Triskeliongirl]

To me your parts have worn out excessively fast, especially the front chain ring, cog set and RD. Usually if you change your chain every 3000 miles your cog set should be OK, but perhaps if you are not maintaining your bike well there is more corrosive damage. I've only worn out cog sets prematurely by delaying chain replacement too long, and then they wear together so both need replacing. I have never worn out a front chain ring or RD in say 10,000 + miles. But I don't trust your LBS, especially because of their refusal to service your hubs. I sense they are trying to rip you off. Get yourself a good book (zinn or bicycle mag or park tools blue book) and start to learn how to take care of your bike!

I agree with Deb on the hub rebuild, the whole point of owning wheels with serviceable hubs is that they can be serviced!