Another point that might actually make more sense is the extent to which you actually mechanic at. I mean if all a guy does is a bit of tune-up, brakes every once in a while, shocks, and a few odds and ends work my thoughts would almost never be a savings for a guy like that. If however you handle just about everything and turn few jobs over to a shop then my way is truely the way for a home wrench to fly!
With that said, I have no idea how far you go with your wrenching activities, I was just trying to understand how you might see things that way.