I had a similar experience with Sportsmansguude recently. I backordered a product that wasn't expected to ship for a month. During the wait, the same product went on sale. Customer service responded to me the same day, and agreed to refund the difference once my product had shipped.
It is not unheard of to price match pending sales, and it really is just the next step in customer service that helps to make the experience better for the consumer.
I have personally canceled orders with companies to get the same item I already purchased at the sale price. It is more work for both parties, and honoring the sale price is often the easiest resolution. However, PSA has bigger issues than this to worry about. And given the secrecy of build components, it may be difficult to price match when the builds may have different parts.
When you purchase an item, that really shouldn't be the end of the business/ consumer relationship. Some businesses go above and beyond to complete the experience. However, with PSA you get the low prices because they sacrifice that level of service.
It isn't to say either business practice is wrong. You just need to know what to expect before you order. With PSA, it is a very impersonal experience, that often involves long waits or incorrect shipments. But you will save money.