I've sorta known this for a short while now but was still unclear how it all fits together. Some clarifications here: http://www.thetruthaboutcars.com/2011/12...ights/#comments Excerpts:
That’s right. The vast majority of mileage results come from internal manufacturer testing to EPA specs, reported to the government and duly republished. Since the penalty for lying to the government in this country tends to be rather massive for anyone not directly involved in the banking industry, one assumes the results are honest. When it comes to Hyundai, however, the issue isn’t quite as clear-cut.