I disagree and think it's 100% the reason it failed.
> A social network's initial frowth phase is completely predicated on it being a space people want to join, and that is accomplished by its delivering value and appeal.
But people did want to join Google+, but they couldn't. And since a social network is only useful if all your friends are on it, people never got into the habit of using it. Why use a social network without your friends? It's not like GMail where it's still useful even if your friends aren't on it.
I can tell you personally that I was excited to get the invite to Google+, only to lose the excitement when only 3 of my friends were on it. By the time Google+ became available to everyone, it was too late. The excitement was gone.
> A cultivated and exclusive club, as with the Haevard Facebook, or early Usenet, has appeal.
The exclusivity of Harvard Facebook succeeded because social media was still in its infancy at the time. Most people didn't have access to the WWW in their pocket yet. Early Usenet had appeal because the Internet itself was still only being used by techies and college students.