It may also be the fact that the players don't need any lead added and not that we don't see it.
They do use the same racquets available for sale, unless a special customization like Joachim Johansson's 18x20, special for him. He also had the 16X18.
I know most of these guys that use Yonex 98 sq in, they use 28in long as well, I think most here know that.
All the women for sure use retail and modify their raquets as they please.