Well think of it this way: the only reason you know the shiny sprites is by hacking the ROM out of the cart, hacking the sprites out of the ROM, or hacking a shiny in (data editors derived from the ROM).
So, GameFreak never intended for you to even see the shiny sprites, so they weren't teasing. They are just there as a failsafe because someone is bound to eventually hack a DS game if they wanted to.