The currently announced mounts are not the only mounts in Pokémon games thus far. The reporter's main draw, the fact that you can now ride Pokémon in a video game, is misleading in the fact that in certain previous titles you could do the same. In Pokémon Ranger: Shadows of Almia, you could ride Doduo, Floatzel, Empoleon, and Mantine. Technically, you could also ride Drifblim and Drifloon, but in a more linear sense, like the HM Fly. In that series next installment, Pokémon Ranger: Guardian Signs, you could ride the three legendary dogs: Raikou, Entei, and Suicune, as well as Latios or Latias, but Latios and Latias had a function more similar to the HM fly, as far as I can tell (I've never played Guardian Signs, but I have played Shadows of Almia).
References:
http://serebii.net/ranger3/rangersigns.shtml
http://serebii.net/ranger2/overworldfield.shtml