Why GURPS Historicals?

The advent of a new Hot Spots volume has reminded me of a question which comes up from time to time: Why buy an historical GURPS book when you can just look up stuff on the web?  It's not just potential customers who ask this. It's a question which keeps the GURPS editorial staff up at night. Not surprisingly, I have a multi-part answer to that question: 1) The premise of the question is flawed.