Actually, a big part of it is that most of the parts come from that region and are available in production quantities within a very short period of time without needing to process the import paperwork (custom forms, clearing fees, duty, tariffs, processing fees, shipping fees) for a large number of individual parts from a number of component manufacturers. It's also a very high level of automation, including fully computerized performance testing of every single unit in both PCB form and finished form. In our case, it has nothing to do with the EPA or taxes.
This also frees up our US resources so that we can build our Petaluma built amps and cabinets with shorter lead times.