Dunno what happened there. USPS started the "shape based" pricing due to the fact that the private airlines charge them, (USPS), the same way. Most priority parcels are shipped on private airliners or on Fed-ex planes.
The additional charge comes into affect when the parcel is very light compared to it's dimensional size.
I've shipped many bows, guns, etc since the change in pricing structure and have not seen a great increase in cost.
As far as USPS being a Gov't agency, that it is, but it does not receive tax money and is self supporting. Which, nowadays, is much more than many private companies can claim.