Powered down and restarted the Comcast cable modem and the D-Link router... still no connection to various the conservative websites ("www.powerlineblog.com", "www.captainsquartersblog.com", "www.hughhewitt.com" and "www.biglizards.net")... most all other websites work fine!
Original question is still unanswered... IS COMCAST FILTERING OUT THESE URLs?
Forget recycling modem, touter, PC, your fridge .... the problem is with Comcast's DNS servers. I've struggled for weeks to get DNS issues resolved. Now I've configured my router to 4.2.2.2, a public DNS server. All is fine now.