Xu Xin's serves were so far beyond illegal. You could see the frustration on Ma Long's face, but he can't call illegal serves on another Chinese player in case he loses and then the person won't be able to serve like that in the finals. Nobody can honestly tell me that ma long would ever miss that many serve returns to a guy he trains with 10 hrs a day. The Ma Long-Xu Xin match wasn't even enjoyable to watch because of the illegality of the serves xu xin was doing. You have to watch for the illegal one. He knows they're illegal too, and only does them at important times of the match when he needs a point. At the end of the match with ma long, xu xin came up with 3 serves where ma long couldn't even put it back on the table. The umpire could have called an illegal serve every time xu xin did that particular serve. Timo struggled with the same serve, because you can't see the contact so nobody knew if it was dead, underspin, or topspin.
I hope at the biggest tournaments the umpires call their illegal serves, because these are the best players in the world, so they should be held to the highest standard.