AFAIK Comcast has about 0.8% of all Internet users.
Are they the largest ISP? What's your source, doesn't seem like something one could guess?
Thanks, 4th largest according to https://gigaom.com/2010/07/28/top-ten-broadband-providers/. China Telecom being the largest with ~60M.
> it vanished for Comcast users whose DNS servers at the time enforced DNSSEC.
I would hardly call Comcast a "weird little pocket of the Internet".