Tracie Egan Morrissey at Jezebel denounces various network TV shows for misrepresenting a study in language development by suggesting that it's about "why women talk more than men," instead of what it's really about: developmental pacing, which has nothing to do with who or who doesn't talk more in adulthood. Indeed, as Morrissey points out, the study can't prove why women talk more than men, because there's no real reason outside of "everybody knows" to believe that women talk more than men:
Still, for her report on the study on this morning's Today, Andrea Canning opened with an oft referenced statistic that women talk three times as much as men, using 20,000 words a day compared to men's 7,000 words a day. There's no explanation or scientific study supporting this. It seems to be wholly made up. But it's managed to stick around long enough to be referenced again and again, making it OK for journalists to continue to use it—like warped version of public domain—without having to cite its original source, of which there appears to be none.
Morrissey briefly links to a wonderful Language Log blog post from 2006, in which linguistics professor Mark Liberman tried to find the source of the claim. One needs to read it to marvel at how far and wide a fake statistic can travel simply because people want it to be true. He eventually traces the claim back to 1993, when there was a flurry of Christian-right marriage counselors promoting the idea that women are gabbermouths and men are taciturn, and therefore ladies need to squelch hopes of having their emotional needs met in their marriages.
Liberman didn't stop at uncovering the urban legend's source, however. He has an extensive archive of examinations into whether women talk more than men, and by and large, a fair reading of the research suggests the answer is "no". For every study showing women talk more, there's another showing men talk more. After a while, it becomes difficult to deny that individual preference and environmental pressures have more influence than gender on how much talking people do. (For instance, I work at home and my partner works in an office. Odds are really high that he speaks many times more words than I do on a regular basis, because he has to.)
So why do people so readily believe women talk more? Part of the problem is that our prejudices distort our observations about reality. Consider that most Americans overestimate how much of the population is gay by a factor of 5 and overestimate how much of the population has illegally immigrated here by a factor of 6 or 7. They also overestimate what percentage of the population is on welfare. Traditional gender roles demand that women should be the listeners and not the speakers, so a woman who speaks as much as a man comes across as talking "too much."
I would hate to be perceived as going on too long, so I'll just add that your reaction to learning that women don't speak more than men is probably predictative of your personal levels of sexism. If your first response is to say, "Nuh-uh!" and to launch into a full-throated defense of the claim, then beware! You may be sexist, and you're talking too much.