How about both sides giving a little?
I am willing to admit that if Serena had gotten that first serve in, Justine might have told the umpire, "I had my hand up."
But by the same measure, if Serena had gotten that serve in and it had been an ace or an unreturnable serve, she would not have said "Oh, look, Justine had her hand up. We must replay the point."
If Serena knew Justine's hand was up, she had to see that before she looked up at her own toss, because you can't hit the ball without keeping your eye on it. So why didn't she just catch her toss. If she didn't notice Justine's hand until after she hit the ball and was already in her follow through, it didn't have any effect on the stroke.
So, let's just move on and look forward to a great final tomorrow.