I think it's true. But they don't have to reply to all messages. It's just because females are the ones who are approached/massaged most of the time from many males, and thus they have to be selective in responding. Also, I think women are less inclined for casual hookups than men do, and thus they get even more selective. As of content, it's hard sometimes to find what to say. And I'm not sure if the content is as important as the first impression of the woman to the man from his profile and photos.