User blog comment:Ohmyn0/Making your wiki HTML5 compliant/@comment-1649337-20120705175934/@comment-957747-20120705200235

http://www.mediawiki.org/wiki/Extension:Math

"'It was a part of the core MediaWiki software until MediaWiki 1.18, r85706.'"

All Wikia has to do is install the extension manually.