Apple thinks the ads that appear on iPhone and iPad are so cool, users would be willing to download an app that is nothing but ads. The iAd Gallery app is the ultimate example of something only Apple could get away with, because of its rabid fans who think everything the company does - even something as mundane and tiresome as selling ads - is amazing.
Just so there is no confusion, the app is nothing but a bunch of banner ads, presented in an image gallery format.
The iAd platform is nothing particularly interesting or noteworthy. Ads are pretty much exactly the same as anything you'd see on a website or Android app.
Perhaps it would be different if there were hilarious commercials to watch, or particularly groundbreaking ad visuals or SOMETHING. Instead, this may just be the most pointless app we've ever seen.
And it comes directly from Apple, which means someone or some group of people at the company had to spend time developing this instead of actually doing something productive.
Perhaps one iTunes user's review is the best summarization of what the iAd Gallery app is all about:
"Tired of apps getting in the way of your adds? There’s an app for that!"