I think that it's not that women are all "friends", it is just that women are more community and socially oriented humans than men are. Women tend to look at things as, "How can this affect us" where men think, "How does this affect me." Yes, this is a generic statement that does not apply to all people. Therefore, when women get together they are more openly social than men are. When men who do not know each other are bunched together, they tend to ignore each other or stuntedly chat about sports or non-threatening topics. Women can more often than not find a common topic to talk about because they are not worried about maintaining their testosterone-induced puffery.