Interesting point. But, however much I think that whole thing could have been handled differently in Serena's match (v. Clijsters, I think, the chair shouldn't have interfered to default the match at the late stages, when no one got hurt, for example,) Serena was actively angry and abusive. She got fined and sanctioned, in retroactively, the way Kyrgios has been, for example. Djokovic didn't do much in the sense of being angry, but he did hurt someone, and that's an automatic default. That's why I think you don't need to add on. When someone gets into a big rant, the ITF can look at later sanctions and fines. What I still don't agree with is that Serena has paid bigger prices. It has actively (potentially) cost her 2 US Opens, and no one actually got hurt.