Why do I care about any of that? I just want to leave a comment on some random blog and maybe read a couple of replies. I have backed out of commenting numerous times because of this nonsense.
If you personally don't care, then it provides no value to you. That's fine. In that case you can hope that the blog allows anonymous commenting, which the blog author may or may not want to provide for various reasons.
And I would hope disqus offers them that choice. But even if it doesn't, there are many users who are not you and whose commenting patterns are not yours, and email collection still adds value for them.
You're making two separate claims, and both of them are very different to the one I originally answered. I'm not really interested in going further with this.
Persistent identity -> password-protected account -> email for recovery.
I certainly wish more places would make email addresses optional, but there is value in collecting them.