Someone missed the point of the statistic. Jobs was merely saying there is a potential to make money via ad sales and we as Apple want a slice of the pie it not, "hey look we are going to be serving a billion ads a day via iAds alone the day we launch."
Pointless pedantry is alive and well on the internet.
Dude who wrote article forgot the fact that it wasn't meant to be exact.
It's called potential, buddy.
Maybe he wasn't 'forgetting' but rather subtly hinting: someday the App Store will require all apps to earn their spot with iAds impressions!
So he should have said zero impressions per day since no apps currently use iAds.
"c) Free apps with other ad networks’ ads."
There's nothing to stop apple from only allowing apps with ads to use their network.