For me, I think the more 'distant' you are from an event in time / space then the easier it is to poke fun. The idea of a relative being raped or murdered and then becoming the butt of a pub joke, for those people involved, such a piece of bad news will never become funny.
I think there's an important distinction to be made here. There is a difference between 'comedy' and the pub jokes that do the rounds after a particular event. For example the Time Trumpet Muppet 9/11 is not even on the same scale as the 'Could murder a chinese' and 'the indian they ordered arrived burned.'
Not that I get offended, but it's the same old "Do you wanna hear a really sick joke?" with the heard-em-before punchlines bolted onto the latest topical news - neither that clever nor funny.
imo Muppet 9/11 and Woody Allen's holocaust references are true examples of comedy derived from tragedy. The pub jokes I wouldn't class as 'comedy'.