Why "following" instead of "joining"?

I have been testing the 7.x commons for a while now using it as the basis for a social networking platform for education specialists. Using the no-core snapshots it's possible to copy in updates into an existing Drupal site (though I think this is probably not the way it was meant to be used).

What I was wondering about is that it seems that commons uses "following" everywhere. In OG (and from what I know about d-o groups) it seems it's was all about "joining" groups, but it seems commons doesn't even use the OG joining functionality.
Maybe I've missed something or maybe this is all documented somewhere. If there is such a place or maybe an issue in project's issue queue that would be useful to read. Otherwise it would be interesting to hear what the thinking behind this is? Is it more flexible to use "follow"? Is the groups approach to rigid? Or is this planned for later? But why then have two different ways of staying up to date with what's going on?

Thanks for any answers in advance and also for working on this.