We can find limited information about iAd in Apple home page. But with the press release they send, we can see some hints
Apple's press release reads: "iAd, Apple’s new mobile advertising platform, combines the emotion of TV ads with the interactivity of web ads. Today, when users click on mobile ads they are almost always taken out of their app to a web browser, which loads the advertiser's webpage. Users must then navigate back to their app, and it is often difficult or impossible to return to exactly where they left. iAd solves this problem by displaying full-screen video and interactive ad content without ever leaving the app, and letting users return to their app anytime they choose."
Apple wants their ads to be with more emotion & interaction.
Sounds difficult to understand... just spend 10mins, and talk a look at the presentation by Steve Jobs, then you can know more.
http://mobilemarketingspd4290.blogspot.com/
