Nick - I think you've hit on a broader philosophical point. DIY is cheaper... IF you know what you are doing. For cars, you do. For cars... I don't.
I can tell when a mechanic is making an inappropriate amount of money off of me (usually their body language and shop conditions tell me). I don't know enough to argue or instruct them otherwise. So I have a "guy" I go to, that I trust. BTW, if anybody has a german car and is looking for a mechanic, I've got your guy (other cars are out of luck, he doesn't like anything non-german and sends them away).
I've found it to be true of food (cooking for real, from scratch, seasonal, preferably from my garden is dirt cheap if not free), home repair (I can manage a lot on my own with the internets and a decent hardware store), sewing (though goodwill kind of makes this moot)... most of life.
If you can do it yourself and you know what you're doing, high quality results are affordable. Problem is, not everyone can be a mechanic, carpenter, electrician, chef, gardener, plumber, seamstress, spouse, parent, AND work a full time job. Maybe a few, but the others will be outsourced.
I think cars, since they're used every day and gas/tolls are pretty frequent for people who use them, have a lot of expenses that people forget about (unless they're in the business like Nick or OC about money like me). I know some people who are car nuts and love them and driving, and no increased understanding (if possible) of costs would ever change their ways (good for Nick's business!). But they're not spending because it's necessary, they spend because they love it.
I don't think they're the majority of the people sitting on the parkway every afternoon, though. Maybe I'm wrong.