Wikipedia is a more or less complex web infrastructure, running on some kind of hardware I don't know but I can imagine of a common type, if not a commodity.
So they can do everything they need by using a production oriented distribution (Slackware, Debian, RHEL, CentOS, Scientific Linux, SuSE, ...) and it's an absurdity to even evaluate Fedora as a computing platform for their needs, unless they have on the web server their human users that struggles for the latest release of OpenOffice. I am sure they have not.
I don't know why they have chosen Ubuntu, I hope is for technical reasons and not a political move, but Fedora has a completely different scope, and I do not want to have a stable Fedora, whatever it could means, as derivatives of CentOS are already on the ground.
If someone whines for the poor choices of software from a stable distribution, s/he could, at first, activates external repositories (oh yes there are! they work!) and then joins the related development communities, I'm sure they'll be happy.
There's a joke that states "Ubuntu is an african word which means: I'm unable to use Ubuntu". I do not want that Fedora will mean, someday in the future: "I'm unable to customize CentOS/SL".