The link relationship should be fn url, but WP is splitting this into an fn class and adding url into the link itself. While some microformat readers may be able to understand this it just plain doesn't make sense.

What about that doesn't make sense? Name and URL are two different attributes, so why should one assume that they are always combined? The reason for them being split like this is because not all commenters leave a URL. In that case, only the cite tag with the "fn" class will be present... there is no a tag. While it is slightly different, you can see a similar example on the microformats wiki.

hcards are also supposed to be tied to a name. Therein lies a real problem because while some people will use a real name in comments, most use a nickname or partial name. This could be worked around by adding a field to the comments form for people to select from either real name or nickname and then the appropriate microformat could be applied.

This is actually not necessary... the hCard spec already handles it. Read the Implied "nickname" optimization section (as well as Implied "n" optimization above that). Depending on the value of the "fn" attribute, different things are implied. Could it be made more explicit so there is less ambiguity? Absolutely, but why clutter up the commenting interface with another input field for something so minor?

Like the WAI-ARIA implementation in 2.7, the implementation of hcards seems to have been poorly thought out. I'm sorry to see that this is included in WP by default as a badly formed hcard is really worse than none at all.

Anyway, I don't use hcards or vcards and I'm sure others don't also. What would be gained with the inclusion of the email addresses? Just an easier way to create a mailing list?