frog, I agree - it is definitely a deliberate thing in some cases, and an unconscious prejudice in others. I really do think we are scary to non-stepmums!
I have certainly thought, in the past, about posting under another name and just saying DCs, in order to get more unbiased replies. But I long ago decided that I won't hide who I am on here - I mean, obviously I want to keep my real identity private and I have on occasion name-changed, but only to post about something non-step-related which contains more identifiable details. I figure there is no point whatsoever to asking for advice if I am not asking 'as myself'. And I have come to think that it is important to stand up as a stepmum. I guess it is like the way some people feel about breastfeeding - I'm not going to go off to the toilets to do it because it makes some people uncomfortable!
In a way, the biggest problem I see on this board isn't about the OW question or even the discipline question (though I agree about those, too) - it is the insistence that every household "should" operate in a particular way, and conform to a prescribed (usually step-child-centric) model - regardless of the needs and desires and capabilities of those IN the family.
I also see a lot of distortion of the same differences that happen across the boards - for instance, parents have different ideas about what responsibilities a child should have at a certain age, or different ideas about how family finances should be handled, or different ideas about the obligation of parents to adult children. Fine. But when those topics are raised in the context of blended families, the motivation is automatically assumed to be a negative one, and any rational discussion is out the window. My values are independent of my status as a stepmum, sorry!