That scenario would make a lot of sense if only because users who buy an iPad will instantly encounter iAd-served ads. At that point, keeping iAd officially under wraps would make little sense.
While the rest of the world obsesses over how good the iPad will be -- the sensible money says that it'll either be awesome, or will suck -- the mobile advertising community will be more focused on any new type of ad delivery system that's embedded in the iPad. As the new tablet device appears to be mostly a super-large iPhone, any new ad platform buried within it can probably be seamlessly added to new iterations of the core cellphone device.
The stakes are high: Google (GOOG) is busy rolling out various new properties in an attempt to secure a dominant position in mobile advertising platforms in just the same way as it dominates online search. Advertisers and their agencies will be hoping that iAd (via iPad, if it's a success) can give Google a run for its money. If it cannot, brands and their agencies will be unable to play Apple and Google against each other for price cuts.
Of course, this all assumes that iAd is coming as advertised. And that's still an "if."