There really is no explanation other than what they call the "standards and practices" department of individual networks. Yeah, there are some FCC rules concerning the issue, but they're complex and have a lot of exceptions.
In regards to MTV and VH1 blanking things like god, bullet, and gun, those I know for a fact are an individual network thing. It doesn't have anything to do with the actual government. Some of the rest of it depends on what time the show comes on and whether it's on a network, cable, or pay channel. However, I think the FCC ruled years ago that TV could show basically whatever it wanted, but that local governments could choose to censor such programs if they felt they were "below community standards." This exact thing happened with my hometown with respect to the show NYPD Blue when it was in its original run... I think they showed Andy Griffith reruns in that time slot every week or something back then, lol. The radio actually has a higher burden of what case law calls "community responsibility," so there's actually going to be more censorship there. I think the reasoning was at the time those legal precedents were set (ages ago IIRC), far and away more children had access to radios than did televisions.
I don't know if this helps or not, but that's how I understood it after taking an introduction to constitutional law course at my community college years ago, lol.
O, why should wrath be mute, and fury dumb?
I am no baby, I, that with base prayers
I should repent the evils I have done:
Ten thousand worse than ever yet I did
Would I perform, if I might have my will;
If one good deed in all my life I did,
I do repent it from my very soul.
Act V, Scene III; Titus Andronicus--W. Shakespeare