According to an unnamed Apple employee: "We periodically review the apps in the iAd Network to ensure that all apps receiving ads are aligned with the needs of our
advertisers ... Currently, our advertisers prefer that their advertising not appear in applications that are targeted for users that are young children, since their products are not targeted at that
audience."
As MacStories notes, Zornek's app, Dex, is clearly targeted to kids playing Pokèmon on their Nintendo handhelds who also have an iPod touch or iPhone. Bigger picture is that "the change could be relevant to developers of apps and, more importantly, games that are targeted to kids, and come as free downloads with integrated advertisements."