To give an extremely general answer, men and women have a different number of words in their daily vocabulary; women have considerably more. I regret that I can't remember the numbers, but have a notion that it may be about 25,000 to 15:000 women: men - it is a serious order of difference though.
Once a person has reached their daily limit, they will naturally be quiet. Obviously, however, there are situations that may come up which require one to speak!
Now, here's the bit that some people find contentious. It's all to do with the fact that our brains have not evolved very much in thousands of years, and that *shock horror* men and women are actually different.
Men tend to speak in very direct sentences and use language in a very tightly defined way. This is because when you're a pre-historic bloke hunting an antelope, you need to pass very precise information to your chums in the minimum number of words. Men have evolved to be better at concentrating on one task at a time.
Women tend to use language in a different way. Women's brains have five language centres to a man's one, which means they can track multiple conversations simultaneously. Because women traditionally took on the role of looking after the home environment, the female brain has evolved to be good at multi-tasking multiple kids and food and relatives plus watching for a sabre-tooth at the cave door. Because of the greater number of people with whom they would interact, there was a need for more words. Women also use words to communicate emotions more than men do, and generally use words in a less tightly defined way.
So, to get to the 'Silent Treatment'; women use words to 'reward' their friends, family and associates, so to be denied them is a sign of disapproval. Personally, I always know when I'm getting the silent treatment, and hate it!
Now, let's see how many people interpret this answer as sexist...