Hes kinda got a point there. You can beat the EPA values with the TDI but its not easy and requires very concise driving techniques.
beating EPA totally depends on the car.
I had a G35 coupe once. on adjusted SAE 2008 mpg it would be something like 17 city 24 fwy.
Even if I babied it for a few tanks, you could maybe sqeuak out 18 mpg combined. Everyone i know who has owned a nissan product with the VQ engine seems to not be able to get EPA milage in it so maybe its a nissan thing. a lot of german seem to exceed EPA milage in "real driving" since they are designed for 55+ mph fwy which 98% of people do since i guess they are autobahn cruisers. Nissan products... not so much. mazda rx-8 um no.
So my last car was a 2005 TSX, 2008 SAE adjusted was 20/28 (or well it was on the 2008 one which is mostly the same car). I could easily get 24-25mpg. ON the freeway up and down CA from norcal to socal could get into the 34-35mpg range.
My latest car has 21/27 and at 70-75mph freeway cruising with no traffic gets about 30mpg.
THe key is to hold rpm about the same, and not speed up or slow down too often, but it isnt entirely about keeping under say 55mph. Some cars are not even in their sweet spot at 55mph depending on how they are geared. Tough I think I could squeak out another few mpg.
Edmunds just tested a stripper 2011 sonata manual. rated 24/35. When i owned the G35 I lived in the same general area as the edmunds office (my ex roomate works for them actually) but they got under 25mpg combined during their test , but I tend to think the fwy milage on the new sonata is a bit ridiculous and is more "we figured out how to game the 2008 SAE EPA rating" than anything.
On another note, the stripper model edmunds had even ewith the steel wheels and plastic hub caps still looks great.