Just to clarify - are iAds only supposed to be implemented on free apps? Or, in other words, is there anything stopping an app developer from including iAds in

Just to clarify - are iAds only supposed to be implemented on free apps? Or, in other words, is there anything stopping an app developer from including iAds in a paid app? Also, do you think a developer would make more money with a free, iAd version over a paid app? If so, developers would obviously be more enticed to offer a free, iAd version, which would also make Apple more money (40% of iAd revenue versus 30% for paid apps).