Creative Commons question

My weblog is currently licensed under a Creative Commons Attribution-NonCommercial-ShareAlike license. I allow comments for every post, subject to my approval. Other persons are therefore able to add their own content to an individual entry page.

The work is the individual entry on my weblog. By adding a comment a person is essentially creating a derivative of the work, an annotation to an entry.

Are comments considered part of the work and therefore subject to the Creative Commons license? If so, I should probably remind posters that their submission is subject to the license. Any thoughts?

Sidenote: Movable Type does not make it easy enough for me to manage Creative Commons licenses. I cannot change my Creative Commons license through my weblog configuration screen, even if I am granting a more liberal license than before. I should also be able to turn on or off a license for a post just as I am able to do with comments or TrackBacks.