Times Have Changed?

The usage between "each other" and "one another" is different. Usually, when there are only 2 persons in chatroom, we say "They are talkubg each other"; while there are 3 or more person there in chat, we say "They are talking one another." It is a grammatical rule, at least 20 years it was so familiar to people, I assumed. And now, I found out there are some writers, used to depict "one another" when there are just 2 persons there. So I doubt whether or not the times have changed.