Wikis seem to have less baggage attached to them and that might partially (and only partially) explain their recent rise in use within the enterprise.
I'd also suggest that part of the reason that I always suggest that Wikis will get faster uptake than things like Blogs and Social Bookmarking is that Wikis can be a better replacement for something else without much behavior change. The first uses of Wikis is as an easier content management system that houses reference material. It could be information about how to use some software, or interesting content that people have collected about a topic, or whatever. It's just a really easy way for a group of people to put up web pages. And, it's easier than dealing with your IT department's CMS package. It's easier than using an HTML editor and publishing your pages somewhere. It's easier than RoboInfo.
Is it widespread among eLearning Professionals? Not really - see Use of Wikis as Compared to Other Tools.