The problem with their reasoning is this:
The regulations that went into effect in 2010 (those that created the need for DEF and DPF) created both reliability problems and fuel mileage problems.
I have a 2001 Peterbilt with a CAT engine that currently has 1.7 million miles on it. The only major repair was a trans and clutch at 1 mm miles. Currently gets an average of 7.2 MPG at 80,000 lbs
Also have a 2010 Peterbilt with a CAT, needed an engine rebuild ("in frame") at 510k miles and averages right at 6 MPG.
One more, 2013 Volvo (with Volvo engine) with "after treatment system" repairs every 100k miles or so. 5.7 MPG
So the problem isn't just with the increased cost of a new truck but also with the additional repair and maintenance costs. The difference between the trucks MPG may not seem like a lot but we're running 94 trucks fleet wide and a difference of even 1 MPG is a huge burden to the company's bottom line.
Only now, with our 2014-2016 trucks are we seeing some increased reliability with the after treatment systems but no increase in fuel efficiency. Essentially it has taken engine manufacturers 5+ years to get the after treatment systems up to a decent (I didn't say acceptable) standard, at the cost of trucking companies. Now we'll deal with it all over again with these new regulations. Makes it hard to make any money.
2014 Surveyor SC321BHTS
2016 Nissan Titan XD SL4x4 Cummins