I have used Comcast cable internet service for a couple of years. I bought my own D-Link modem since they are very cheap, and use a Linksys router/wireless access box. To my knowledge there has never been a computer connected directly to the modem.

I don't think your Comcast rep is giving you the whole story. However, the initial setup is very complex and the $50 you pay to the network tech to get it right the first time is probably money well spent.