My first reaction was one of slight astonishment. The people responding were regular consumers of science fiction, and we're talking about a webpage that over the course of the past six years earned three Hugo Awards, four Nebula Awards, and a World Fantasy Award for their writers and editor. So how is it that there are people who hadn't heard of it until now?
I don't know the answer, but I can take a few guesses, although some of them are probably wrong.
First of all, I don't recall SCI FICTION doing much advertising, or having much of a presence at conventions other than the Worldcon. As I noted before, the Sci Fi Channel seemed to view it as more of a loss leader, a way to bring people into their website by offering content not related to their shows. (To their credit, they are still doing this quite nicely with their Sci Fi Wire short news pieces and their nonfiction news and review page Science Fiction Weekly.)
Secondly, despite the inroads the web has made over the past few years, in some ways it's still a very small part of the overall culture. True, everyone reading here is on the web, but a lot of people may not have been using the web as their primary tool to seek out short stories (such as docorion who, bless his soul, noted that he "subscribe[s] to Analog", but had never heard of SCI FICTION).
There's also fragmentation. A lot of places provide short fiction on the web; the more that exist, the fewer people any one webzine can draw. It's like the fragmentation of television into many channels. The series finale of Friends didn't draw nearly the numbers that the series finale of M*A*S*H did, because there were so many more options for television viewers.
As for my original lament, it's possible that I'm looking at a very skewed sample. Right now, I get most of my on-line interaction via my LiveJournal Friends list, and I do try to keep everyone in my Default View, just to get a feel for what's going on in people's lives -- even with people whom I've never met but who "friended" me because I write science fiction. (Hey, if you're curious about me, I tend to be curious about you.) Now, the nice thing about the Internet is that it has allowed formerly isolated writers to form communities for support and discussion. But because of this, when I dip into my Friends pages, it often seems as if everyone in the world is a writer or aspiring writer of science fiction -- and I know that that isn't really the case.
So in the end, the main reason that I may have been assuming that only current and aspiring writers were lamenting the demise of SCI FICTION is that many of the people whose blogs I read regularly fall into that category.