CBS and NBC "We ain't gay."

I'm trying to figure out CBS and NBC's stance on declining the United Church of Christ ad. I get that allowing gays in the church is a controversial topic, but to say that they're rejecting it because its an "advocacy" ad, and that because "the Executive Branch has recently proposed a Constitutional Amendment to define marriage as a union between a man and a woman, this spot is unacceptable for broadcast." The first is just silly coming of an election cycle, and we see advocacy ads everyday. The second is just weird. First, the ad doesn't even address gay marriage, and second, does this mean when the amendment comes up CBS won't allow any ads on the topic? I'm not crying censorship here, or suspecting any conspiracy, but I think the reasons are just plain odd. My pet "wacko theory" is that CBS is trying to make nice with the White House after the National Guard memo fiasco. My realistic guess is that CBS and NBC didn't want to deal with the backlash, boycotts, and loss of other advertising for airing the ad. I think its cowardly, but they are running an business. Only thing I know is that the reasons given don't make a lick of sense.