Did you see where that couple drove a 2009 Jetta TDI over all contiguous 48 US states, something around 9,000 miles, and averaged 69mpg! Amazing! I don't see why they don't build hybrid diesels... I'd assume 100mpg could be possible, in a real car...
Nope, didn't hear 'bout that one. But you're right... in theory, the automobile manufacturers could easily build something like that.