David Strom:

"Another problem is the cable companies themselves, who look at having multiple PCs attached to their cable modems in the same way that the phone companies looked at having multiple residential phones in the late 1960s. Charging extra for additional PCs is just nonsense, and yet one additional reason to purchase a firewall/hub/router product, or what I call frhub in my book."

I didn't know David Strom wrote a book (Home Networking Survival Guide), sales at Amazon look OK (it ranks at about 25,000 as I'm writing this).