I can attest to that. I have not nor ever will tell any female in my orbit what size my boyfriend is. Bottom line, it's none of their fucking business. To begin with I believe in intimacy and keeping private the sexual relationship I share with my guy. Add, I don't trust other women. Blame it on actual personal experience of having an ex-boyfriend cheat with, at the time, a good friend. Unfortunately for that daffy bitch the guy in question had a micro dick and she got what she deserved.
Seriously though, why would I ever tell another woman my boyfriend's cock is big and that our sex is amazing? I'd be just asking to attract a bad element into what should always remain a private matter. It's like telling everyone you won lottery, just fucking stupid. It's blood in the water for the sharks. It increases the potential for attracting some envious greedy dirtbag to come gunning for what you have and they want. Keeping your mouth shut is always the best policy.
As to the OP question ...
I'm going to take a crack at this because I do believe there are some women who lie about it. I've certainly been in the presence of at least two women who came across as phony upon conveying to a group of other females that they'd been with hung guys. Both were terrible liars. One was even called on the spot by another woman who had slept with the same guy and knew he wasn't hung but average. So I ask myself, why would these women lie about it to other women? And why would some women lie and share this information with the men they were currently having sex with? This is what I came up with ...
Obviously not all the women (nearly half in the study group) who took part in the question posed in the link have had 9+ inches. More reliable scientific studies of penis size (if any actually exist?) certainly don't support the numbers seen in the OP link. But more importantly the study the OP posted is highly flawed as there is no real proof that only women voted. I think it's safe to say a significant number of men corrupted the vote. Having said that I still think there are women who voted 9+ who never experienced anything close to that size. So again, why?
I personally think it's just a matter of some women wanting to either one up their female friends or impart to their boyfriend/husband this lie in order to establish a level of control. It's a way a woman can (falsely) establish experience that is beyond her current partner's capabilities which in turn creates this circuit of power for her within their relationship. Once they reveal they've been with a man bigger (which to a lot of men immediate translates into better) they instantly create control in the bedroom. At anytime after making this information known she can then use it as an emotional weapon as it relates to his masculinity, his ego. The man is left to wonder if he's ever good enough in bed because of this.
She can use this "ace" during heated arguments to instantly cut him down. She can also slow pitch it and simply act coy and play it off as something that she'll tell him really doesn't matter, but the question remains, why then did she plant the seed? And there in lies this invisible level of control as she can then through seemingly innocuous dialog, simple inflection, imply, mood during sex, continue to reaffirm this sexual seed of doubt she planted in his psyche.
The perfect victim for her is one of those guys who continually needs to know and already had issues with size and inadequacy. Men who will feed her questions about the "big guy" she supposedly had must be like a drug to a woman who enjoys creating such twisted grids of control. It's a clear indication to her that she's in his head, in control of his very manhood. The relationship becomes this process of building him up and tearing him down. There are some women who get off on that. The reasons for her doing this are vast but it's always about power. It a pretty wicked thing to do to a guy and the type of women who play these games are clearly insecure, sexually immature, and well, rather disturbed imo.
For me, if say, I moved on from my current boyfriend I'd never tell the next guy he wasn't as big as a previous lover. It's a really cruel thing to do to create this feeling of physical inadequacy in a new partner and only works to deflate him as a man. Considering I'm into very masculine men who are dominant in the bedroom I'd be just detracting from the sex, this sexually prowess and confident beast, the archetype that I adore, lust for, as a lover. I imagine some women have issues, baggage, and feel the need to crush a male ego in order to elevate their own lacking self-worth but in my mind all you're doing is hurting your relationship by injecting this doubt in your guy's confidence. How does that benefit anyone or make for a healthy relationship and good sex? Personally I want to build him up because in the end it goes to making him a better lover and strengthening what we have together. I want him to be the best he can be not some emotionally unsure puppet that I take out and play with from time to time.