Don't be hatin', I'm just telling you first hand experiences of people I know. There's a guy on a diesel truck forum I visited a while back that got HAND CALCULATED 33mpg in a Dodge 2500. The truck had an 8 speed transmission and custom air dam to improve aerodynamics. A man with a 3500 dually reported 28mpg. Driving smart get's a lot of mileage. I've seen average mileage on my computer as high as 27.5 mpg empty. Sure, the computers are usually a couple miles off, but that ain't bad. Yes, you have to coast a lot and not rev it up high when you accelerate, but to say it isn't possible is just not true.
I've read articles about guys getting over 100mpg out of Toyota Priuses, which have an EPA rating of 45-48. Driving style has lots to do with it.