Originally Posted by BreakPoint
Del Potro never used a K-Factor. It's a paintjob. He uses the old ProStaff 6.1 Classic underneath the paintjob. A racquet which came out in 1991. Wilson hasn't made them in a very, very long time, which is probably why Del Potro can't get any more.
Wilson do not make any racquets that proffesionals use as they are all custom made.
Players wont just 'switch' to different racquets when Wilson decide to bring out a new line for business and marketing reasons, it does not work like that. Players like a certain frame and their companies ensure they are getting it.
Ask the players on these forums, most including my self play with a certain racquet with certain strings and tension, we do not change because it is what we are comfortable with and works best for our technique. You cannot expect Pro's to change, unless is major like what Federer has done recently.