Yes, it is legal. The only episode they've aired a cut version of is "Road to Rhode Island". Another episode they'll probably air a cut version of is "A Hero Sits Next Door". Apparently, FOX doesn't like jokes involving airport security, Osama bin Laden, and JFK pez dispenzers.
Maybe it something to do with Seth MacFarlane was going to be on one of the planes from Boston that hit the Twin Towers, So it might be he doesn't find Bin Laden as funny as he used to