I'm sure it has to do with the factory being in a free trade zone. US (for example) based companies can take materials and basically import the goods to the Taiwanese free trade zone, have the goods manufactured by Taiwanese workers, and then immediately re-exported to the US (or wherever the stuff is going) without paying any duty or tariffs on either side. Countries allow these free trade zones and the importation/exportation without tariffs because it brings in jobs which boosts the economy in the host country more than the tariffs alone could do. The US also has free trade zones and they provide jobs to Americans just the same as Taiwanese free trade zones provide jobs to the Taiwanese. Though I don't understand why anyone would really use US free trade zones considering the harsh taxes and fees associated with employing US workers in America.
The only cost is shipping which I'm sure is mitigated by the lower labor costs. What they get in return is a quality product probably produced faster and cheaper than could be done in the states. The factory can also more than likely handle an ever increasing work load and the obligatory work space necessary and spyderco doesn't need to pay the overhead found here in the US including property taxes, health insurance, high construction costs, etc. associated with the stifling economic conditions found in the US. If it were cheaper to expand here in the US and employ more US workers with better technology and better abilities to hire employees who do quality work and fire employees who do shoddy work without fear of litigious attorneys watching everything a company does, then I'm sure the Golden plant would be massive already.
I applaud Sal for keeping quite a bit of what they do here in the states in spite of all the obstacles set in front of them.