There was a modest amount of Internet Fussing after Apple released its iAd Gallery app. Business Insider noted that iAd Gallery appears to violate App Store guideline 2.13, "Apps that are primarily marketing materials or advertisements will be rejected," and MacStories echoed that sentiment. Inneractive noted that a third-party developer had her app rejected for doing basically the same thing that Apple's own iAd Gallery does.
Out of all these outlets, Inneractive is the only one that focused on the real point; the third-party developer clearly had the idea for an iAd gallery long before Apple released its version, and it's unfortunate her effort went to waste. There may have been more to that rejection than meets the eye, though; it's likely that some of the iAds advertisers wouldn't have been pleased with their ads showing up in a third-party "gallery" app without their consent, and as Rene Ritchie pointed out this might have been a plausible intellectual property argument against the approval.
But even if Apple's iAd Gallery would have or should have been rejected if it was a third-party app, the key point here is it's not a third-party app. Apple doesn't have to follow the same rules as third-party developers. For instance, Apple can use private APIs and frameworks as much as it wants, and its home-grown Weather and Notes apps show it has no problem whatsoever with releasing apps that have "limited functionality" (snap).
You know why Apple can get away with those things while third-party developers can't? Because Apple owns the platform. Let's look at this from another angle: say you're renting a house, and your landlord has a strict "no pets" policy. You drive by his house one day, and you see two giant Great Danes patrolling his front yard. Are you going to knock on his door and say, "Hey, how come you can have pets, but I can't?" Of course you wouldn't -- but if you're game enough to try, please film the attempt and post it to YouTube once you're no longer homeless.
Expecting Apple to follow the same rules it's established for third-party developers sounds faintly silly to me. Apple developed the entire platform, from iOS itself, to the hardware that writes iOS code, to the servers that run the App Store, to the App Store itself, to the hardware that runs iOS and its panoply of apps. Apple created the entire iOS ecosystem from end-to-end, and it developed and single-handedly supports its entire infrastructure... yet some people believe the company should be held to the same standards as one developer who whipped up a quick app to show off iAds.Sorry, but it doesn't work that way. Apple built the house, and it owns the house. The rest of us just live in it.