I THINK I know the answer to that but I'm worried I must be wrong because I seem to be more concerned about this than most people.
To me, a blog is software that enables a person to post thoughts/opinions/essays, and have others respond. I might post a book review and have my peers give their comments on the book. In another blog I might send a committee the minutes from a discussion and ask them to comment on what steps we should take next. All of these I have done with students. The common thread here is that I post and others comment. This is what I see in many of the sites provided as examples.
To me, a wiki is software that enables groups to edit the same document. Wikipedia is the most known, but also most appropriate example of this. The whole is more than the sum of the parts is the theory here. When people work interactively, they are inspired to create something that wouldn't have been created had they simply added parts, or posted comments. Many of the wiki examples I see do not contain this critical aspect of peer editing. Instead, many wikis are blogs posted on a wiki site. I find the history and discussion tabs of a wiki to be the most underrated and underused aspects of the wiki software, but they are the most unique and fascinating. Again, to me, a wiki should more resemble a google doc than a blog.
In online adult classes I have taught, my students are very, very reluctant to criticize, change or comment upon a classmate's work. My HS students are less reluctant. Asking them how it feels to have their work peer edited, they comment that they appreciate having someone help them.
Sometimes it's difficult to tell if the wiki site has been created as an edited site by a group of members b/c without a membership you aren't permitted to see the editing--ie teacherlibrarian. So I can't always comment on specific sites. Some sites are a collaboration without much editing, but that is better than the blog response wikis I see so often. For example, the St. Joseph's site is collaborative but probably not much discussion, debate or editing is done. That's ok by me because the end result is a collaboration. I find the same in the albystaff wiki.
I like the discussion in the student wiki example This shows these students were collaborating and debating.
If I look at the history of the blog and only one user (usually the teacher) has posted, then I think the wiki is underused.
I agree that even for simply commenting the wiki page flows better than the blog page which can be harder to navigate. I can understand why someone would use wikispaces over blogger for that reason alone. I just wonder if I'm the only person who makes that distinction between the two types of software, and thus activities.
All that said, I'm impressed with any class using either wiki or blog software. I'm just splitting hairs.
