It doesn't necessarily increase the amount of skill required, but what it does do is increase the amount of physical strength, self belief, confidence and focus that is required to do it time and time again over a 3-4 hour period.I also don't understand the OP's point that somehow this can be done without great skill. Absurd. It INCREASES the skill required to play. Perhaps the OP somehow confuses skill with the artistry or complexity of points, which seems a common misperception.
Wow, remember when we were all saying how boring a 5 1/2 hour match was?
Guess we were right.