I think the invites are better in this case.
The author made a similar point of Google+.
Essentially, by not letting anyone in right now, and only having invites. That means no one can come in now and see it as a barren wasteland.
When they send out the invites, they'll probably send it to all the people who registered at the same time (hopefully a lot by that time) and when they all join on at once, they all see each other online. No wasteland problem.
When they send out the invites, they'll probably send it to all the people who registered at the same time (hopefully a lot by that time) and when they all join on at once, they all see each other online. No wasteland problem.
Seems like a good solution to me.