There is absolutely no way for wordpress, or any other website for that matter, to absolutely verify the identity of a commenter. It simply cannot be done.
1. I use someone else's computer to post a comment on your blog under the computer owner's name and email address. Even if you somehow required an email verification, I have access to the other person's email program (assuming they have automatic login set in their email program) and I can then confirm the comment, and then delete the email. I have just posted a bogus comment on your blog and deleted any easily identifiable tracks.
2. I use the above computer to post a comment using my information? How can you verify it is really me? I'm on a different computer, perhaps in a totally different area, or perhaps in a totally different country.
3. I have three computers: one at work, one at home, and a laptop I use for traveling. I comment on your blog from work, I comment on your blog from home (different IP addresses) and then I take a trip to Istanbul, Turkey and make another comment on your blog under the same username and email address. The IP address is now in another country. How can you verify that it IS or is NOT me?
4. Now, I head to Paris, France and post another comment on your blog from my iPhone. How do you tell if it is really me? You cannot.
5. IP addresses? Completely meaningless for the most part since ISP's now do not assign unique IP addresses to individual users. Each IP address could have hundreds of users assigned to it. The main reason this is done now is because of costs. It simply is not feasible to buy large blocks of IP addresses so that each user can have a unique address. And besides, with wi-fi hot spots all over the place, and everyone using smartphones and laptops and netbooks, it simply isn't possible to track and verify a users/commenter's identity.
6. One last example: From my home computer, I can log onto 4 different wireless networks that neighbors have since they have left them wide open. Again, how can you verify that it is me making the comment?
This is one of those problems without a solution I'm afraid.