Edit after the questionnaire added additional information:
Apple will reject your application if the iAd is inside a table cell. iAds should be in a static position on the page, and not in any type of scrolling (including tables). This is due to the fact that iAds pays for the impression, as well as a click, so the presence of iAd in the table view cell will restart it whenever it scrolls again on the screen, which can be many times. This is similar to click fraud or similar behavior. Apple will not allow this.
Perhaps because your request is not working. Put a breakpoint or some message in the failure delegation message that is sent when requests fail and you can see if it will be called.
IAd requests may not work for several reasons, including iAds are not available in your country, there are not enough resources to complete the request, an ad has already been shown after this session, etc.
Perhaps this displays on the Simulator because the Simulator does not have any concept of its location (for example, Maps always show your location as the Apple HQ in Cupertino).
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