Large providers like those are being blocked for ident because they are the source of a LOT of bots. Most bots won't ident, so this measure helps to cut down on bots.
As far as saying Comcast is the biggest provider, you're incorrect. AOL still holds that title. Although people are much better off using ANY service other than AOL considering how bad the AOL software is for your computer.
Anyhow, open/forward port 113 on your router and/or firewall(s) and you'll be fine. Otherwise, try to connect to other servers on the network. Usually, not all servers require it.
