Biggest problem is the way they are tested, under strict lab conditions, the "highway" test for UK cars does not exceed 42 MPH, when the speed limit is 70, its not wonder the fuel figures are almost impossible to acheive in the real World.
The EPA had to change how our cars MPG is calculated back in 2008. They were severly overestimating the MPG of cars by 10+ MPG in some cases. 99% of average Americans could not get close to the estimates.
Only people who followed basic hypermiling techniques could do it.
Don't think for a second this isn't a get out of jail free for Hyundai... They knew the EPA was investigating and was going to do something about it... The EPA could have thrown a ridiculous fine at them (think Toyota unintended acceleration witch hunt magnitude) and then easily made them pay out double or triple the "compensation" they're giving to their customers as part of this "settlement."
What's sad is that even though Hyundai was the biggest and most intentional offender, the next worse offenders (all of them American) will avoid a wrist slap, nor will there even be a precedent set for penalties since the EPA no longer has to do anything about it.
So Hyundai's web site offered me about $87 dollars for the 22k miles I drove last year. That is their assessment of how much I would have over paid for gas with a -2mpg adjustment? I am going to run my numbers when I get a chance and see what I come up with.