Fuel mileage...with a bale mover

I found this post on a popular agricultural discussion board the other day. Long story short; a hay producer in Nevada bought a bale mover (pictured) and drove it back to the farm. It was an 8 hour drive, going 55 mph the entire time, running the (diesel?) engine at 2750 RPM. As you can see, this rig has NO aerodynamic efficiency whatsoever.

His fuel mileage? 15 miles per gallon!

Now, if a bale mover can get 15 MPG at full RPM, why the heck can't Detroit put out cars and trucks that do better than this? Emissions controls are probably a big issue, as the bale mover is an off-road application, and therefore not fully subject to emissions controls (although they might have Tier III controls in the future, the same as new semi trucks today).

For those of you not familiar with bale movers, they are specialized machines that will pick up the small square bales our grandfathers and fathers put up (and caused our fathers to leave the farm for less strenuous work, like operating jackhammers), stack them, and then transport the stacked bales to a shed or edge of the field. Not many are used in Iowa, as we prefer the round bales (invented by an Iowa State grad student, no less!), and the West Coast horse and export market prefers small square bales.