Some quick analysis gave some interesting results:
$ for site in boston.com latimes.com cnn.com neu.edu mit.edu www.whitehouse.gov www.fbi.gov sony.com slashdot.org google.com reddit.com craigslist.org blogger.com myspace.com amazon.com w3c.org php.net; do full=`lynx -source http://$site | wc -c` comments=`./htcomment -q http://$site |wc -c` echo "$site is"`echo "scale=4; ($comments/$full)*100" | bc`"% comments" done boston.com is 16.9600 % comments latimes.com is 5.5300 % comments cnn.com is 1.6200 % comments neu.edu is 15.2600 % comments mit.edu is 2.6600 % comments www.whitehouse.gov is 5.8500 % comments www.fbi.gov is 4.5900 % comments sony.com is .7300 % comments slashdot.org is 3.7300 % comments google.com is 0 % comments reddit.com is 0 % comments craigslist.org is 0 % comments blogger.com is 2.7500 % comments myspace.com is 17.0700 % comments amazon.com is .2600 % comments w3c.org is 0 % comments php.net is .3400 % comments
Unfortunately these numbers are not 100% accurate -- htcomment can't differentiate between "kjdflakjfdaf " and just "", so the numbers for the sites that do have comments can be a bit skewed in some respects, but it is a good first order approximation. It is no coincidence, in my opinion, that google, w3c and craigslist have 0 comments on their frontpage. For sites that have >5% comments on their frontpage alone, you can't help but wonder how the behavior of their site or their bandwidth expenses would change if those comments were filtered out at their edge, or never put there in the first place.