There's a post on the Drunk Duck Forums about why artists should update. Here's my two cents (totally blowhard pompous):
I think frequent updates show a level of commitment to your comic, this
site and your readers. Readers are busy and you often have one chance
to get their attention, so the more you post the better your chances.
Comic readers have always been fanatically loyal (look at your
newspaper) and that can have a couple of different results which I show
1. Calvin & Hobbes was written and drawn by one person who had such respect for his medium that he fought his syndicate for five years to prevent the characters from being marketed. He had tremendous talent and dedication and was rewarded by people who religiously read his strip. He felt a duty to the readers to produce the very best he could do every time (which was, barring two sabbaticals, every day for almost eleven years).
2. Garfield. This strip was created by one person but is now produced by a team of writers and artists. It was never very funny (IMHO) but has slid into positive crap-ola. The writers steal gags from Charles Schulz, Watterson, Walt Kelly and a host of others (and it's still not funny). They reuse tired old gags and market the character in every conceivable way. They obviously figure that, because people read it anyway, they don't need to be better.
Most fall in between. In webcomics, almost all of us are unpaid. The only way we can show our respect is to produce whenever we can. I hold down a full time job, am raising a family and play in two bands ...and I'm holding myself to a rigorous (insane) schedule of full-color weekday updates. Haven't missed one yet in over 70 strips. I figure it's the least I can do.