In which the question, "why do they do that?" arises in relation to cats

I found myself in the position to watch the water bowl last night. Moonshadow comes in, and crouches down to drink. I'm aware that his drinking behavior has always been a little peculiar. He walks stiff-legged as he approaches the bowl. He may tug at the side of the bowl repeatedly with his paw, or he may pat at the water, and then lick the water off his paw. Sometimes, he plays in the water, alternately patting, licking his paw, and shaking the water all over the vicinity. I picked him up after last night's session; his front paws were soaked, and his chest and tummy were damp.

After Moon got his drink, Alexander comes in to drink. He crouches in front of the bowl. I have watched him before, and I know that he seems to have trouble lapping up the water. He holds his head almost flat to the surface of the water, and laps a couple of times, then lifts his chin and licks and swallows two or three times, and then laps, lifts his chin, and so forth. The result is that his chin is totally saturated with water by the time he is done. This time I noticed a behavior that I've never seen before - Xander would reach around the water dish with his right paw and dig in his claws (to little effect on the linoleum) and pull himself around the water dish - while drinking - to the right. This of course took some time, since he spends more time swallowing and licking than actually lapping. By the time he was done, he had pulled himself about a third of the way around the water dish.

Of course, I'm asking, "why do cats do that?" Googling "cat drinking behavior" didn't get me much, other than the standard admonishions to always have fresh, ample water, and close the toilet, yadda, yadda, yadda. One site said that cats will stir the water with their paws because the sound and movement are stimulating, and another said that a cat's unusual drinking behaviors are normal and should not be discouraged. But no one can actually explain why they are doing that!

I know why they drool, I know why Hershey liked to suck on blankets, I know why they bring half-dead mousies into the house, I know why a seemingly-contented cat will suddenly turn on the hand that's petting it; I know why they knead, I know why boy cats will bite and scratch hands scratching tummies, but girl cats generally like it. But why do they drink in such funny ways? They don't all do it - it just seems that my two do it. Are they broken?