SevenofNine, the reason Serena was booed this weekend had little to do with all the resons you cited. This was a specific case, not a general attitude. What happened was this:
When it became apparent that Serena and Venus were going to meet in the Semis, another tennis player, when asked what she thought the outcome would be, said, 'Ask Richard, it's up to him' or something like that. She expressed what many have been suspecting, that the Williams family orchestrates the outcome of the matches between Serena and Venus.
Then, before they could play, Venus who showed absolutely no sign of injury in her previous match, suddenly announced that she could play in the Semis. Coming right after the accusation that the family decides who will win, it looked like a set up to let Serena get to the finals.
Not only did the audience not get to see the Venus-Serena match they paid for, there was suspicion of throwing a match. That's where these boos came from. If a white tennis player had pulled the same dirty stunt, they would have been booed just as loudly (witness the way Martina Hingis was loudly booed during last year's French Open, for instance, even though she is a popular star on the tour).