Of course this sort of thing still happens regularly at entertainment venues all over the world. But it usually involves hecklers who aren't well known, so it doesn't make the news.
What I find interesting about this incident is that it illustrates some of the conventions of live comedy. Firstly, that the medium requires that audience members know what to expect. And like so many entertainers now, Strassman is pretty racy ("dark and edgy" as he puts it) and uses profanity in his act.
What's fascinating is that Mr Grant didn't know what to expect. This is very surprising, since Strassman is very well known in Australia. He's performed on Hey Hey It's Saturday! and other Aussie shows countless times. But even if you were not aware of Strassman in particular you'd still expect a bit of rough language, surely. Pretty much anything that's funny nowadays also has a bit of swearing in it.
Like all hecklers, Mr Grant was oblivious to that other main convention of comedy: respect. Even though it's not like serious theatre, which has a "fourth wall" and demands silent deference from those watching, live comedy still needs a bit of respect for the performer for it to work. The performer addresses the audience directly, conversing with them in a way, but it's still a scripted performance, and a lot of work and preparation have gone into it. The polite thing to do if you don't like a performance is to just exit unobtrusively. Sure, it's reasonable to complain back at the box office, or even ask for your money back. But to actually disrupt the routine itself is really rude, particularly when the crowd is clearly enjoying it so much.
One wonders if this guy would have done the same thing in the middle of another kind of show. Would he get up out of his seat and then walk onto the stage in the middle of a drama and berate the actors? Somehow I doubt it. Everyone knows that kind of behavior is just not on.
But it's okay to do it at a solo show that's getting laughs. It's always the way with comedy, isn't it? It just don't get no respect!