Among younger juniors there's a lot of topspin moon-balling that wins matches. At the more advanced levels, especially on hard courts, less moon balling takes place.
There's also a certain level of mythology you'll hear about net clearance in the professional game that simply isn't true. I've heard people claim that 3-6' above the net is standard for the professional men. On hard courts at least this isn't true. I try to get out to professional tournaments when I can. Usually the average rally ball is hit in a window from 1' to 4' over the net with a lot of pace and spin. Some players cut it much closer and you'll see multiple shots in a set tick off the top of the net cord.
I don't think the pros are aiming to net skim, but it is a result of driving the ball hard with a lot of topspin. The modern drive forehand has a lot of vertical component to put speed on the ball and the spin helps keep it in the court. This necessitates hitting fairly close to the net. The higher net clearance shots are used to drive the opponent back, to mess with a bh, or to give the hitter time to recover. Even Nadal can easily rip a 90mph forehand within a foot of the net when he's going for a winner.