There is research to show that men are sexually attracted to a female "friend" (see Kaplan & Keys, 1997; Swain, 1992). Bleske and Buss (2000) make the case that "friendship" is perceived differently for men than women in their research "Can Men and Women Just Be Friends). Though there is no conclusive evidence, the few studies I can find tend to point in that direction. I think my theory still holds water. Other than a gay friend, male friends (not all) I would argue have more of a sexual interest in their female friend than the woman realizes.
I agree with your theory mostly. I think one major component missing, however, is that your research takes a unilateral approach as you have asked dozens of women, but what about the men they are referring to or even just men in general? Their answers to you are merely speculative, whether accurate or not, and may be based on several factors (i.e. truth, perspective, an inflated opinion of ones self) because you are not asking them if they would sleep with their male friends, you are asking if they THINK their male friends will sleep with them.
Further, I wonder what kind of women you have surveyed. Smart? Beautiful? Sexy? Overweight? Homely? Average? Single? Mariied? With or without kids? I think you will find that the answers will vary with a balanced group.
I think male/female friendships can be successful but I think the older people become, the more difficult it is, for many reasons, number one being the stigma that is put on these relationships by partners (boy/girlfriends, fiances, and certainly spouses). Given the cultural changes we have seen over the last 30 years especially, I think it is probably more prevalent now given that there are far more women in the workplace vs. a workplace that was primarily dominated by men prior to then. Previously, women were at home while the men worked so men and women wouldn't typically meet unless the purpose was for romance. Even still today though, I would say that male/female friendships when spouses are involved are rather difficult to maintain even if the friendship existed first.
Studies show that sexual tension is present in 62% of these relationships which is a big reason why many don't work after one or both people become involved in a romantic relationship but even still these relationships can be successful and mutually beneficial. Men appreciate what they get from women that they don't get from guys (i.e. men typically group together and don't talk much about feelings) and women appreciate men for what they don't get from other women (a more relaxed atmosphere where you are not expected to take on the emotional burdens of others every time you are together). Not to mention, what generally attracts a man to a woman who becomes his friend begins physically, even though that may not hold true for the woman.
So, I think they, in most cases are a woman's friend in addition to being a boyfriend in waiting...I definitely see a co-existence there. :) I could go on and on about this I think!! LOL