Ownership of blog comments?

I'm working on a project that has lead me to a dilemma...
If someone posts a comment on another person's blog (like this one, for example), is it ok for the owner of the website/blog to then reproduce that comment?

A number of my comments on the Creative Review blog have been published in their magazine, so I'm guessing they have circumnavigated any legal issues, most likely with their extensive terms of use page.

How does this cover @replies on twitter? If someone posts replies to my requests, do i then have the right to reproduce those replies in any format?

If anyone has an opinion or any info on this I would be really grateful.
(i promise i won't reproduce your responses.)