I've just added Webcomics Asylum to the list of blogs focused on webcomics. It's one of the mysteries of the internet that we didn't bump into each other before.
Jack Carter's been covering webcomics for a year and half, and has a sizable archive of interviews and reviews.
He gives an interesting report in a recent post: of fifty webcomics he's reviewed since starting, 24 have stopped updating. I can tell by the roster he likes to cover less well-known comics, as do I, but that's a pretty high attrition rate. The idea of doing a webcomic often sounds better than it is. It requires an incredible time commitment, and a lot of people jump online without having done a lot of comics on paper, so they get tangled up and quit. (Suggestion to those choosing their domain names now: Consider doing a ten or twenty page story on your first outing, so you can produce something finished before you run off with your friends.)
Of course, if you want to see a really high attrition rate, look at blogging. Never in the history of the world have we generated content so much faster than eyeballs.