The main difference between other products and PING though is that other products are not exclusively custom fit. Every PING club sold is supposed to be custom fitted. If PING didn't enforce prices people would go to a real world retailer, get a fitting, and then order from the cheap place online. By making the price the same everywhere, the sale now comes down to service rather than who will discount the most, or give discounts to certain groups.
As has been mentioned PING do actually do a rebate for military. This being the case, things are even more confusing. Why would the shop not just explain about the rebate and let PING cover it? That way the customer gets a discount and the store makes more than by giving there own discount.