Some years ago Matt Cutts answered the following question: “How does Google treat sites where all external links are no-follow?”. he didn’t respond to the question but he talked about wikipedia.
Consequently, we installed a nofollow chrome extension to highlight in red nofollow links on pages and then we decide to display a Wikipedia page. We discovered that all external links from Wikipedia.org were still nofollow today. Exceptions where external links to websites belonging to the
Then, we typed the name of this engineer who is the co-creator of TCP/IP into the google search field. And Oh suprise surprise! the wikipedia page is in first position in Google. (see below)
It means that even if all links on the webpage are nofollowed, the wikipedia pages rank really well in Google.