This is not true. Read the terms of service before you claim
anything:

http://www.comcast.net/terms/use.jsp

"Prohibited Uses and Activities Prohibited uses include, but
are not limited to, using the Service, Customer Equipment,
or the Comcast Equipment to:
[...]
14. run programs, equipment, or servers from the
Premises that provide network content or any other services
to anyone outside of your Premises LAN (Local Area Network),
also commonly referred to as public services or servers.
Examples of prohibited services and servers include, but are
not limited to, e-mail, Web hosting, file sharing, and proxy
services and servers;"