You're underestimating the amount of rich parents who're willing to buy a console even for only one game because don't forget that Christmas is the most lucrative season of the entire year so Super Smash Bros. for Wii U alongside Pokémon OR/AS they'll be selling like hotcakes, whether it's John Lewis, GAME, GameStop, Selfridges, HMV, Tesco, Argos or a different retailer they'll most likely have a hard time keeping stock of both games for too long during this season.
No, you're overestimating the pull that demographic has, not to mention the general interest in the Wii U or Smash Bros. Just because there are parents who could easily afford such a purchase doesn't mean they'll be willing to, especially considering the fact that the PS4 and Xbox One are in far greater demand.
There'll certainly be people who'll buy the Wii U for Super Smash Bros. for Wii U during Christmas plus including how popular the series is, it's illogical to think it'd sell less than a million copies.
Good thing nobody said otherwise. Stop moving the goalposts.