In the latest version of CFormsII you can require that the person sending you an email/comment/etc. includes his name, email, and URL among other things. But people registering for your blog only have to include their email. I want to know who has registered for my blog, and where he can be found on the web. I want to know something about registered users, and an email just doesn't do it.
To be blunt, user registration for WordPress blogs sucks. Please upgrade.