Wikipedia introduced the no-follow tag, presumably as way to prevent people using Wikipedia to pass link juice. Even when most Wikipedians wanted no-follow removed, Jimbo Wales, the founder of Wikipedia, hs chosen to keep no-follow.
It seems that all Wikipedia links are not what they appear to be, however, as TechCrunch discover:
“It seems that while the nofollow tag is added to the standard outbound links, it isnâ€™t applied to inter-wiki links, including links to Wikia, Wikipediaâ€™s for-profit spin off. For example, on the Wikipedia page for Wikia there are a number of links to Wikia pages which do not contain the nofollow tag”
That appears very sly and SEO-ish, I must say. Hoarding the link juice and directing it towards your own web properties.
“We have heard back from Jimmy Wales and he has stated that he was opposed to the nofollow policy and had only dropped his opposition to nofollow on advice from Google and others.“