Looks like that particular Comcast server / site is deliberately configured to not respond to ICMP based ping packets. This is not an indication of anything wrong.
Hmmm... This is what you stated earlier. If you want to try to improve the stats, can you remove any excess splitters that may be in the line leading directly to the modem ?
Try pinging pretty much anything else right now. both comcast.net and www.comcast.net seem to be in DOS defense mode and after 3-8 pings jump to the 100's of ms or fail to respond at all. Normal usage seems to be fine, of course different areas maybe at different response times.