I've never signed up to receive a bloggers post in my email box.
Although I have commented, I have never been asked for anything more than my email and name.
If you can refer me to a site that's asking I can take a look.

Open ID doesn't mean "any ID"; it's a special service where you sign up for an account that you can use to authenticate yourself for many different sites without creating a new ID for each one.

Forboystoo, a lot of Blogger accounts now require this kind of authentication, so I'm guessing it's the default now if you don't change it. I presume it's meant to stop spam, but it stops comments, too.

I only have one blog I read that asks for this to comment and I use Google Acct. You do have to open an account.

If you read some blogs where anyone can comment, the there is a tendency for lot of comments which are hostile, illiterate and off-topic. By asking for some form of identification a lot of this is eliminated.