This is happening to me also (version 6.3). How do I completely turn off comments? I've even deactivated the comments module and that hasn't done anything.
So this has been plaguing a client of mine in v7+. On finally digging down I have found out how to turn this off but it is BURIED!
from main dashboard in backend, go to content->news; then under "Manage also" comments for news on right hand side (rhs), click that then click "Settings" when rhs reloads under "Settings for comments" then expand "commentable types" under the left hand side tree that appears and click "Telerik.Sitefinity.News.Model.NewsItem". Uncheck "Allow Comments" then save.
Note to Sitefinity - I love the granularity.. hate that it's so buried :P