Sue, I think it may be partly because when we first started chatting on the initial thread it was obvious that our needs were different from those of the posters on some of the other diet threads. We accepted right from the start that we were coming from a different place, where self-esteem and background was an issue, and we accepted that our mindsets were what needed changing in a way that some dieters don't find. I think maybe it was that which appealed to some of the longer-standing members of the MoFos far more than just joining one of the other established dieting threads. It probably takes a little while to get used to that idea if you're used to a more standard, "eat less, move more" approach to weight-loss.
Plus as you say, because we already recognised that our needs aren't the same as, say, the Lardy Ladies or cod's bloater threads, it may have been easier for us to open up about some of our issues, and try to work through them.
My self-esteem is very, very low but on these threads I feel as if I matter just as much as anyone else, and that's a big thing for me. It's probably because we've chatted lots about the issues we have and we feel confident that no-one's going to mock us or take the piss if we open up and talk about what's behind it all - because most of us are in the same boat.
I think that it can be hard to break the habit of seeing some foods as bad and therefore seeing ourselves as bad for eating them - and I think that a lot of the established slimming clubs are at fault for perpetuating the myth that there are good foods and bad foods.
I do think it's extraordinarily sad when people say that they would be a "better person" if they were losing more weight/not eating "bad" food/not bingeing. Maybe it takes a bit of practice before we can separate the act from the person and realise that being fat or not controlling our food doesn't equate with being a bad person.