I just wrote this in a conversation on Heidi's excellent blog, but that thread is getting a bit old, so I thought I'd repost it here. The whole thread is well worth reading.
This is educated guesswork, but here's how the comics market seems to break down in late 2007, to me:
Superhero readers are divided between those who prefer trade paperbacks and a still-strong contingent of readers who follow single issues month to month. From the continuing sales of singles, I assume that those readers are not bothered by the common net complaints of extended plot threads or lack of "enough content" per issue. They still like buying their comics every week and following continued stories as they come out.
Indy comics readers, in contrast, have largely abandoned the single-issue format. They prefer a larger chunk of work and are willing to pay for it. For most indy publishers, including (I'm hearing) Slave Labor, singles are no longer worth the expense to publish.
There are, of course, exceptions on both sides, particularly for long-established creators with an existing following. It's definitely true that if fans really want to read a new comic -- any new comic -- they'll follow it to the format it's published in.
And along those lines: I seem to be the only one, but the new LOVE & ROCKETS format mystifies me. I understand the impulse to try something that fits the material better, but this strikes me as combining the high price of a trade paperback with the short shelf-life (and lack of bookstore salability) of a single issue. Sam Henderson tried something similar a few years ago with, I recall, disastrous results. ACME NOVELTY LIBRARY works, but that's a real art object. And I say this as someone who will buy it -- I'd buy LOVE & ROCKETS if it was stencilled on the side of shipping containers.