We argued about this quite a bit, and the end thinking is that condoning the trip hack steps our foot in territory that should likely be stayed away from. The line is already getting blurred with texture and music hacks, as well as infinite replays, but those hacks are within the boundaries of being cosmetic and not actually effecting the physics of the game. If you start to allow hacks that effect the physics of the game, you could potentially be opening a pandora's box.
As an aside, having the rule expressly against tripping also saves some hassle. I remember back at Pound 4 me and Y.b.M. were suppose to play Ninjalink's team. NL has had occasionally used Ice Climbers, and in addition to that Kirby is mostly an aerial character and my movement was largely with dribbling, so tripping would only minimally effect our team. To shorten the story, we had to insist with NL not to play on his trip-less Wii and had to justify our cause not to play on it and wasted a good 5-10 minutes arguing before we could even sit down for the match to start. At Pound 4 hacked Wii's could be requested not to be played on, but even though the rule was in our favor it was still a headache and caused a waste of time.