The part that I don't get in all these articles is that Williams was playing against a WOMAN. How can it be sexism? A man didn't win the match, a woman did. Whether the call was wrong or not, Williams whining and crying about sexism is complete BS.
Putting that aside, Naratilova is right -- its never a good argument to say that you should get away with something because someone else did. That's an argument made by people with no character, which describes Williams well. Another commentator called Williams a bully. That is an apt description of what she did to the young lady who won.
The claim is that the rules on interchanges between player and official are applied unevenly between men and women’s matches. I have no idea if the charge is fair or not.