You see, last week Iranian cleric enlightened the world by explaining the link between women who show off their assets (so to speak) and earthquakes.
"Many women who do not dress modestly ...
lead young men astray, corrupt their
chastity and spread adultery in society,
which (consequently) increases earthquakes"
lead young men astray, corrupt their
chastity and spread adultery in society,
which (consequently) increases earthquakes"
The only logical conclusion I can come to is that Fox and ABC must be terribly frightened of earthquakes, and thus for the safety of their viewers do not wish to air the ad... 

PS - if you would like to test the theory that cleavage results in earthquakes check out this blog for details on the upcoming BoobQuake event.