I agree with lakedude, and would add one more:

The third part of the reason is that the truck owner does not have a big fat display sitting on his dashboard telling him he's not getting what the EPA said he would. Ignorance is bliss, as they say.

Get rid of that ignorance, as hybrids do, and it's a different story. I have a friend with a new Subaru with a mileage meter on the dash, and guess what?

- He's not getting what the EPA says
- He's unhappy with the car regarding his mileage

I think if the whole world had their MPG glaring at them from the dashboard, there would either be a lot more unhappy campers, or else people would realize that the EPA numbers are just estimates and may not reflect reality in certain cases.