Just to add further rationale behind these "rules" - In any form of climbing - the proposition is very straight forward - could you get yourself from point A, to some higher point B, using only your physical strength and prowess?
If you get 20 miles in to a marathon and run out of gas - you just stop running and call it quits. In climbing, however, if you fail - you would likely be killed, or at least seriously injured. Because of this inescapable fact, safety systems get used. In general, the goal is for them only to act as a backup. If you get to the top without putting your weight on the backups, then you've answered the fundamental question of whether or not you could climb the objective in question.
Said "rules" may change a bit, depending on venue. Some people climb very difficult walls, that may be anywhere from 50-200 feet tall, and a 5 minute walk away from the car. In this case, any incidence of "cheating" by using the equipment to take your weight means, "you failed this time, try again later."
However, when people are climbing peaks or mountains, many miles from any kind of help or rescue, the rules may get bent a bit in the interest of beating out a storm, or just plain getting through a tough spot without risking injury. When this happens, the saying goes, "there is no cheating, only lying." You basically own up to any aid you may have used along the way, and no one will judge. Nothing's stopping you, or someone else, from going back another day and trying again for the more coveted "clean" ascent.