But that's the problem.
How would the 3.7l and I5 (the engines that are actually in the CC/cutaway) fare any better?
If anything, those two engines would fare even worse, compared to the V8 and V10.
Rico, I've been trying to dance around a blunt answer that makes my point clearer for fear it will sound harsh, but since we are not making progress, here it goes.
In my opinion you are looking at this backwards. A 3.7L V6 is in many ways a detuned 3.5L V6. They are very similar engines except for the turbo which creates more power and more torque at the expense of much higher BMEP. and while that extra power and torque may feel great to the driver it comes at the expense of higher stresses.
If both engines were running at same 100 HP at 2500 RPM then there isn't much difference, but when the commercial driver puts his foot into it, the turbo engine can produce about 50 percent more torque. That will make the vehicle accelerate or climb a hill faster but it comes at the expense of higher stresses. So in my opinion detuning the engine by removing the turbo limits how much power the driver will use on average. They may end up using more RPMs in the long run to offset lower torque, but apparently that's not deemed a problem.
The diesel may be a different issue entirely, but in my opinion limiting the V6 engine to something like 260 lb-ft of torque instead of 400 lb-ft is not a bad thing other than reduced performance (which is less important to commercial buyers). Like you said, it doesn't reduce fuel economy so why not?
Many private owners on the other hand will buy higher power and torque because it feels better to drive. It's really a luxury few "need" but want anyway. Businesses think differently -- it's more about the bottom line.