It's mentioned in the article. OpenID was convoluted to users. They don't link their identity to a URL. An email address on the other hand is a widely accepted

It's mentioned in the article. OpenID was convoluted to users. They don't link their identity to a URL. An email address on the other hand is a widely accepted identity handle. I understand that FB and TW are rocking for your clients. But that's not the point of the post and why it's a plea to developers. It hinges on the idea that identity is too important to hand over to Facebook. Again, unsure if you read the entire post. It's a very forward looking post and does not focus on what's easy and accepted today.