Ok, if it is a conspiracy and the auto manufacturers have the technology but just won't let us have it:
Why wouldn't ONE company sell out and be the one car maker out there selling cars that get 50-100mpg and just clean up the major market share?
GM, Ford, Honda, Hyundai, VW....
Somebody would market ultra-high mileage cars if it were easy, it's not.
You still have to work within the laws of physics, there is no magic.
The amount of work done to push a 1988 Geo Metro down the highway at 65 mph is about the same amount of work it takes to push a 2012 econobox down the highway. The marginal gains made in drivetrain efficiency get eaten up by the increased weight for today's safety standards and creature comforts.