Isn't that an argument in favour of using Facebook? One account for the whole web, rather than one for each individual blog.

I prefer name and comment, no registration system

No, it's an argument for not requiring an acount when it's not necessary. E.g. for simple comments.

I came up with the following: email is optional, and used for notification as well as editing/deleting the comment. Assuming the email is used for only that, I think that's as convenient and fair as it can get.

Isn't that an advantage of third-party commenting, like FB or Disqus? You get the advantages of registration but without having to do it everywhere.

You assume every site uses either of those two. The reason I made the comment I made is because I keep running into unique systems

Disqus lets you comment anonymously, or log in with Facebook, Twitter, Google Plus, or a Disqus account.

Sounds like you didn't even bother reading my comment. I am well aware Disqus can allow anonymous commenting as an option. But that doesn't clearly address what I stated.