Americans do drive guzzlers (on average). I'm just saying that even those Americans who lust after a nice European-style gas sipper, couldn't buy one because they're not on offer. Interesting to see how consumer "choice" is always smaller than the manufacturers would have you believe.
And if the price of gas were to suddenly go up to $20, it would break many families' budgets (see previous comments in this thread). We'd like it differently, but the reality is that we live in an infrastructure which has evolved in a less than wise way - and yes, there is a large literature about how that came about, and the role of car manufacturers in the process of building suburbs. But that was then, a previous generation. This is now, and the question before us is, given this infrastructure (that we can't all escape by piling into cities), how do we reduce our carbon footprint?
A European-style carbon tax would go a long way towards that. Citizens' Climate Lobby proposes a _revenue neutral_ carbon tax, which gives an income tax rebate that benefits low-income families more than high-income ones. Sounds fair to me. (But maybe this is for a different thread).
About the EPA numbers: those are in line with the MPGs reported by real users at fueleconomy.gov, so that's averaged over many users and the variety of terrain in the US.
EU advertised MPGs are invariably higher than actual MPG reported by real European users, sometimes off by up to 40%. It's really a scandal. It's also commonly known: most dealers (at least Dutch ones) will tell you explicitly to ignore the number on the sticker, and proceed to tell you the real MPG. There is huge pressure to get that g CO2/km number low because so much tax money depends on it.
The annual car test checks for emissions of exhaust pollutants other than CO2: things like CO, NOx, etc. Also important to keep low.