Fuelly...
2012 Hyundai Elantra average fuel economy - 7.8 L/100km
2012 Mazda 3 - 7.3 L/100km
2013 Dodge Dart - 8.1 L/100km, I'd take this number with a grain of salt at this point, 5 cars on engines that are likely not broken in yet.
2012 Chevrolet Cruze - 7.1 L/100km
I think what it boils down to is that some cars do better in the real world than others. Considering that Elantra only has one supposedly fuel efficient engine, while Mazda still has the old less efficient 2.0 and the gas guzzling by today's standards 2.5 in addition to their Skyactiv 2.0, and Cruze has a standard 1.8L engine, an eco tuned 1.4 turbo, and a performance tuned 1.4 turbo.
My car is rated 7.7/5.0 and I'm averaging 7.1. My car has only stepped out of the city once, an 80km trip out to the valley. I have an Ultra Gauge which is a pretty accurate fuel consumption meter, at 100km/h, I'm using 4.5-5.0L/100km. It increases to 5.5L/100km if I go up to 110km/h (I haven't gone faster yet lol), drops down to 3.5-4 L/100km at 80km/h. The American highway numbers for a manual 3 is 39 MPG, or 6.0L/100km.