I think the reason why they separate the Pokemon and the Mega Stone, is to make both sides happy - the players side that wants more wi-fi events, and the Gamestop side that needs more people visiting the shop.
The event is kinda pointless, though.
It's like the Electabuzz/Magmar one all over again - aside from event collection purpose, why do I have to bother downloading one if I can just breed a 5IV one easily? Not to mention by breeding I can get Quick Attack into Pinsir.
And breeding also gives a chance for the offspring to be shiny.
Meanwhile, Japan is currently having a Shiny Jirachi event AND a Surf Pikachu event.....