The Chronicle of Higher Ed's latest article on wikis (subscription required) examines how different disciplines view its authenticity. An excellent point is how historians are not usually collaborators on articles and publications whereas scientists are. Therefore, according to those cited in the article, some scientists also feel more comfortable with wikis. This is along with their knowledge base on "less abstract" notions than historical concepts and events - ie what is more important than the facts and the dates associated with something or someone? Historians often cite the lack of contextualization as a major weakness of wiki articles.
Most importantly, existing case studies of student use of wikipedias demonstrate what underscores student use of this source - their thinking that EVERYTHING is on the web and often an ignorance of the need to compare and contrast a variety of sources - including evaluating the author's credentials and support of his/her arguments - to come up with their own original thoughts and analyses.