Wikipedia has added the NOFOLLOW attribute to their outbound links to help fight spam link submissions to their user-editable encyclopedia.
Some are for this, others are against it.
Either way, I think if Wikipedia isn’t going to share link popularity/equity with other sites for whatever reason, why should others share it with them? Thousands and thousands of sites are linking to Wikipedia passing along link popularity, and Wikipedia is now basically saying “Thanks, but we’re not sending any link popularity back”. I get that it’s to thwart spam, but it doesn’t mean we shouldn’t treat Wikipedia like it’s going to treat us.