This article by Tom Spurgeon does a really nice job of breaking down the direct market's purpose, potential, and problems in refreshingly unhysterical (ahysterical?) terms. I have a similar feeling about the worth of this market: Without comic shops, I'd have "aged out" of reading comics in my twenties, too.
I'd add a couple notes to the "scheduling" section. This issue tends to get heated very fast because it's actually two very different problems with related, self-reinforcing reactions. Fans hate late comics because, well, they want their comics, and because many of them grow to adulthood with the gradual realization that institutions they've trusted (parents, Presidents of the United States, DC and Marvel) aren't perfect and, in fact, sometimes do bad things. Late books are a very simple proof of a broken contract. And because the draconian newsstand distribution system of the '70s and prior made late titles almost unheard of, their current presence is evidence of a Decline in Overall Professionalism. (Which it's not, really. It's just that when Gil Kane or Neal Adams was late, the company would slap in a fill-in or a reprint.)
Late comics are a different and serious problem for retailers, especially cash-strapped ones. Comic shops budget tightly on nonreturnable product, and a late title -- or, to be precise, a high-profile late title -- can cause them real trouble, especially when that book misses its solicited ship date by months. It's therefore in retailers' interest to rile fans up about a popular title that's absent from the shelves for several months at a time. And the retailers' understandable agitation justifies the fans' feelings that the companies are screwing them.
Despite this, as I've said before, there's no evidence at all that fans stop reading late books. Readers read books they're interested in and stop reading books they're not, whether those books come out as solicited or months later. (Tightly-plotted crossover titles are a special case, but even there it's not clear the interest goes away unless the order of books published is seriously compromised. I don't think anybody's sitting on unsold copies of the later CIVIL WAR installments.)
There are ways to deal with late books; I used most of them when I was a full-time editor. And they should be dealt with, for the sake of retailers' fiscal health. But this topic kicks up a lot of smoke that obscures the real issues.