TC, those pipes appeared only in that game, they only emphasized that you were playing PiT, it seems that every pipe in TMK used those kinds of pipes, that needed four people on it at the same time, but in other games, Mario stands on the pipes and goes down with no prob, so those pipes only exist in the Mario and Luigi universe. And, if some pipes are unusable, why would they be built? Just as a little decoration? The pipes in the Adventure mode in SSBM weren't usable probably because they were"Out of Service" Or "closed" So they put slabs of wood on top to prevent usage.