Most services with primarily user-generated content have already covered their bases; check out the reddit ToS ("Rules of Usage," item #3) or digg's ToS (item #6) which dumps all their content under the CC umbrella.
Yes, but I dont think the blogging systems have this since every blogger would have to have his/her own TOS and could not be covered by a blanket wordpress or typepad TOS.
http://reddit.com/help/useragreement http://digg.com/tos