>- Due to its debut before Generation V in Zoroark: Master of Illusions, it can be seen as a parallel to Lucario, which debuted in Lucario and the Mystery of Mew, prior to the release of Generation IV. Unlike Lucario, however, Zoroark was revealed at the same time as its pre-evolved form.
>- Coincidentally, they both share the same names in Japanese and English versions of the game, are in the Field Egg group and need 1,059,860 Exp. to reach level 100.
Source
If Game Freak did the same with Lucario, then it is safe to say that they just wanted to do it that way. This was most likely done to promote Gen. 5 and give a preview of what was to come.