You wouldn't necessarily know this until you had done the described change, but Ubuntu's packaging of Gnome Shell is in various small but annoying ways not as polished and together as Fedora's.
That might partly be because Ubuntu has thrown its effort into its default Unity, while Fedora has put effort into its default Gnome Shell.
Even softpedia provides a way to do it: http://news.softpedia.com/news/How-to-Install-GNOME-3-on-Ubu...