I agree, shame on the oversight for the diesels, just because not everyone makes one doesn't mean they should be overlooked - fuel prices are now similar (actually diesel SHOULD cost less, as gas is derived from diesel like products) and their efficiency kicks gas engines butts in the same size engine, the reason they rule in heavy duty (towing) pickups and big trucks.
I have a VW Passat TDI, and routinely average around 44 in widely mixed driving, and I'm not sure you can get less than 35MPG average with it unless you sit and idle all the time. Highway driving on flat roads is consistently above 50MPG (often way above that, approaching 60 at secondary highway speeds (60mph), interstate speed driving usually averages 43+, not something a Prius can do at 80mph. And this is in an engine that never needs to shift from high gear on almost any non-severe terrain (even high altitude) and putts along at around 2000 RPM, a VERY pleasant benefit after you've driven one compared to the usual tiny 4 bangers and loud CVT motors in terrain that's a little hilly, etc. and keep the transmission very busy and driver annoyed.
Oh, by the way, this car/motor holds the Guiness Book record presently for "gas" mileage in "hypermiler" driving - 78MPG over 100Km. The European brands all have diesels that are as good or better used widely in other countries, we just decide in US for some goofy reason these aren't "clean" engines we can sell here, even if they're getting 50+MPG. Even sadder, the American brands already have them too everywhere but here.
My Passat's a very nice car to boot with good European style handling, lots of room, decent price, and even better it's a truly US car, built in Chattanooga TN, and the price premium is mostly tied to them upselling the trim packages in the Passat - can get Jetta and smaller TDI cars (same motor) for extremely competitive prices, esp if you factor in longevity of the engines (300K mile lifespan is not unusual).
Similarly my wife drives the Touareg 6 cylinder TDI, and though that's a very expensive SUV and can be legitimately knocked for that reason, it's also an awesome engine, tons of power and easy to get over 30MPG highway (28+ avg) in a tank of an SUV well over 5000 lbs (and 7500lb towing capacity - try that in a typical 6 Cyl SUV). Feels like it could climb a tree when you punch it at low RPM. The Passat sounds a little bit like a Diesel at idle and low speed driving, but with the Touareg it's really hard to tell, you have to really listen hard to even notice.
These cars in this review are all good, but it's not fair to leave legit contenders out of this comparison, esp with the tech that goes into the new clean diesels. And don't knock them for the exhaust additive, I don't pay a nickel for that til after 30,000 miles, and even then only needs added about every 10-12k miles, and there are pallets of that at all local parts stores nowdays due to diesel pickups wide popularity. Tip up a jug and fill the little tank and you're done. Worst thing you can knock that for is it makes you think a cat peed on your shrubs if you happen to be around the tailpipe when it injects some into the exhaust every so often lol. Let's price compare when the battery replacement cost comes due for the hybrid and the diesel engine has 50% of it's life left at same mileage. This is the up and coming class of engines really, rather than the hybrids which is totally dependent on battery technology. Don't forget these are also turbo engines, also keeping their size down and performance up.
But once battery tech gets good enough, forget hybrids and maybe even diesels, we'll just have battery cars with tiny little generator engines (probably diesel...) as the most efficient engines as our econocars, getting routinely 100MPH+ -- sans government stupidity and politician interference, of course.