False. If you put a short-torso chick on a mens frame with appropriate TT length, the ST will be too short. It's less of a problem than getting the right size ST and having too long of a TT, but it's still not right and "just get a longer seatpost" isn't really a proper solution to that. I also can't describe how much I hate the term "marketing device" being applied to this. women's specific geometry is a solution to a widespread problem, one where the audience is very appreciative for the fix. Yes, it gets more women on bikes, thereby selling more bikes, thereby turning more profit for big T, but that doesn't make it without merit as "marketing device" suggests.
To be fair I may be a bit biased against WS design by the experiences my SO has had with them, which has been a universally bad fit. She isn't a novice to riding either with about 7,000+ miles a year in the saddle and a full race calendar... all on "men's" bikes. But, her level of bike experience doesn't mean that she has universally applicable body geometry. In practice, many frame manufacturers steepen the seat tube angle at smaller sizes (I'm curious why that is done, it makes no sense as it isn't a rear end geometry issue), which cancels the supposedly shorter top tube. The WS design is basically a correction for poor frame design. If they simply scaled down the same geometry, the bikes would fit just fine because the stack and reach would scale accordingly. The actual differences between mens and womens frames is maybe 1 cm at a 54 cm frame size... about the variation of stem length change in a typical bike fit, and not an unreasonable amount of seat tube length change. So, for very small women, WS may make sense, but the small mens frames won't fit small men well either for the same reasons.
At the end of the day, I always support the bike that fits best. If the OP finds that the WS geometry fits better, then that is the bike for them. 100%. If WS design brings in more riders for commute or recreation, then that is fine too. But, I just haven't seen it making a huge difference with the many women I ride with.
Or as Gerard Vroomen puts it (designer for Cervelo, who has many frames in active duty in the pro-racing world):
Building bikes for women
Unlike many companies in the bike industry, Cervélo does not build a frameset specifically for women. "I really can’t ride the women’s bikes as they’re made by the mainstream companies," I commented. "That’s because you are a woman," quipped Vroomen. Vroomen has strong feelings on this subject, and recognizes that he is working against the grain. "It’s based on the theory that women have long legs and a short torso. The only problem with the theory is that it’s just not true," said Vroomen of the approach to building women’s bikes adopted by many companies in the cycling industry. The framesets designed for women tend to have a shorter, steeper geometry and an upright position. "That’s not performance cycling, that’s riding around and going to the bakery," argued Vroomen. Sometimes, you need a bike to get to the bakery.
But the bakery is not a bike race. "The women’s geometry, it makes some sense for people who aren’t that serious about the sport," noted Vroomen. He conceded that the marketing is very powerful all the same. "It’s such a strong story, you go to someone and you say we made this bike just for you." Still, building a bike for a small person is the same whether that person is a man or a woman, according to Vroomen. "If you look at a guy that’s 5’5" and a woman that’s 5’5", they have the same ratio." Vroomen called his bikes "small person specific." A smaller size frameset is simply different than the bigger sizes. After all, "that’s why we have sizes."
We need to "debug the myth" that women need separate bikes, Vroomen believes. Some women may want a more upright riding style, as may some men. But that preference is separate from dialing in bike fit for women. In fact, he worries that the current marketing narrative may actually turn some women away from the sport rather than helping to build it. This set of ideas, "it’s completely destructive to women in cycling," he said with only a touch of hyperbole. Certainly, sponsoring a women’s team offers Vroomen a tangible way to make the case for his approach. Garmin-Cervélo team rider Emma Pooley stands 5’1" and rides a 48 cm Cervélo S3 frameset.