Thanks for all the replies. I guess it's good to get an idea what every body else does and to see that my experience is so different.

As far as replacing the chain goes, I've been told that you should change it every 1000 miles, and have come to believe this to be true since I usually start to get a hint of shifting troubles (chattering, grumbling, skipping) after about 900 miles. The troubles will get worse, and when I bring it in to the shop, a check with the chain check tool confirms that the chain is stretched. I am aware that road grit (and too much lube) can cause excess wear to the drive train, so I do take pains to clean, lube and wipe the chain after pretty much every ride. I suspect that the problem in this area has to do with being a heavier than average rider on hillier than average terrain.

This would also apply to brake wear. I can testify that the brake pads were worn down to the nubs at the times they were replaced. I think they are probably softer pads than I had on my other bike (which didn't need to have the pads replaced), but these brakes work soooo much better; I had to resort to the "flinstones" method of braking (with the feet on the ground) in order to fully stop with the others.

As for the cassette, I've also been told (from sources independent from my LBS) that after 3 chain changes, it should be replaced. I believe that as well, since I was experiencing chain slippage and shifting troubles in certain (favorite)gears. The mechanic wasn't sure if the front rings actually needed to be replaced, so the estimate to replace them was a "worst cast scenario".

It's possible I've over estimated some costs like tubes (and yes, SK, I could patch them since I still have them) and have forgotten yet other things I spend money on. I don't think my LBS is taking advantage of me. I'm guessing some of the extra expense is just the cost of being an extra heavy rider...