I agree with clencher, there is no way cars would run as clean as they do today without the current regulations. I am excited to see california regulate emissions on the smaller engines too, that sets a precident for other states. It is too bad though that the smaller diesel cars have not made it over here.
Consumers have not really gone wild over efficient cars. I am not sure we have the intelligence to drive development in the right direction with our purchases. Honda used to make a really fe small simple affordable car : the vx, but because demand was low, they switched to hybrids (which i guess are more exciting).