I am watching the 2012 Men's Table Tennis championship between Timo Boll (DEU.) and Ma Long (CHN.). I've never really watched a professional table tennis game, and one thing that I am seeing these two players do quite frequently is rub the inside of their hand on the table throughout times in the match. At the 15:28 mark in the video -- after an incredible rally -- both players partake in this practice. There are several instances before this point in the game, and presumably after as well, that they rub their hand near the net. In each instance both players have done it - close to simultaneously. I don't know if it has anything to do with "being ready", but it reminds me of in Soccer/Hockey when the referee has each keeper raise their hand to signal that they are ready to play.
Why do these players rub their hands on the table near the net throughout this match of table tennis? Is this related to a rule of any sort? Or is it more of a habit that professional table tennis players have adopted?