There's a second issue in play beyond the DOT requirement, which is indeed very valid and why there is a low GVWR option on some vehicles. The axle ratings are the most each axle can be loaded to. It's remarkably uncommon to have a load that brings both axle to just their rated weight. It's far more common to have one axle heavily loaded while the other axle is lightly loaded, for example a big plow on the front or a heavy fifth wheel right over the rear axle. The GVWR takes this into account, and the load capacity of all of the other systems on the truck - power train, brakes, steering, etc.
In my opinion the axle ratings are the last thing you look at, and only when you know you have an odd load. It would be very rare to be under the GVWR and over an axle load rating.
Brian
