I too tend to get about 5 to 7000km of life out of my chains--but I do keep them wiped and lubed regularly and I'm not riding on wet muddy roads all the time. I take care of 5 or 6 bikes in the household so I've got the whole rag wipe of chain, pulleys, cassettes and chain rings down pretty fast.
It's kinda like keeping the kitchen clean, if done regularly then keeping it clean is fast. If you don't touch it for a week, the piled up dishes and dried up mess takes you a heck of a lot longer to clean.

A reasonably clean drivetrain is always going to last a good deal longer than one that you ignore, so cheaper, plus it shifts nicer, looks nicer (it you care about that) and its always good to be intimate with your bike, you tend to pick up on problems before they get to be a problem.