You make a fair point. Some people do care about brands, and would like to interact with them.
But I don't think this is the primary or even a very important part of social networking. My point was that TFA far overestimates their importance, going so far as to cite it as a deciding factor for G+'s success or failure.
What about rock bands, video games, movies, radio stations, operating systems, charity groups, regional festivals, political parties, etc., etc.?
I think most people are emotionally invested in at least a few of these kinds of non-person entities and it's not unreasonable to think that they would like to follow them on G+.