Yeah platform advertisements are usually selling the dream because frankly the s/w is rarely there on launch.
I'm speculating here but there is also probably media production issues involved here too, you need to be able to produce a complete media campaign across multiple media with clear consistent imagery and message during your launch window. Making an individual game or games central to that massively increases your risk, take Watch Dogs and PS4, Sony and Ubisoft were so in bed together they offered a Watch Dogs PS4 bundle on launch but then Watch Dogs slipped. It didn't force Sony to pull or rework their print and tv campaigns for the PS4 because the Greatness Awaits campaign relied on no single game, whereas if the trailer was cross cuts between WD and PS4 extolling the virtues of both you'd have had to ditch that entire campaign.