The difference lies in that companies think that Facebook users are an audience which is there to listen to them (aka. eyeballs), whereas a normal user is on Facebook to interact with their friends, to share photos and funny stories, organize parties and share their thoughts. With friends, not with companies. But brands, in their pursuit to monetize the "audience" somehow forget that it's not them the users are here for. And so they ruin the experience for everyone.
It should be acknowledged however that today for most people some commercial entities are "friends". If a small publisher I like publishes new books, my favorite sport team has some important news, etc., I'd like to know about it, and Facebook slowly became the best facilitator of such "friendships". I think it is somewhat different from normal advertising, and was slowly transforming the perceptions of the commercial entities themselves.
But now, FB has strated breaking that model, differntiating between human friends and the other (paying) kind.
I don't think most people want to limit their interactions to their close social circle. The Dallas Mavericks have 2+ million likes - I'd guess a majority of those fans would want every single update they make in their feed, and would value those updates much more than the photo of an ex-coworker's baby making a mess. Do they want Walmart updates? Probably not, but I think the Twitter model for the feed works better for users than the Facebook model (unsubscribe to things that clutter your feed).