Depends upon the volume of each builder, under 100 units a year there is no federal sound standard. There is however an EPA (smog) standard that is based on back pressure. The standards are pretty loose actually, the EPA and ARB make it sound complicated and restrictive. For the most part, to meet these back pressure requirements the exhaust will be fairly quiet-or at least acceptable.
Most of what your seeing I would bet are consumers that have already changed out the stock exhaust for something that makes more noise.
As an example; Big Dog, Arlen Ness, Big Bear, HellBound and others all come from the factory with a quiet exhaust. People just change them, same as a stock HD.
