Music videos do not have the same copyrights as CD's or movies. Because record companies are distributing them as promotional material and are shown for free on television, they can not make the argument that they are losing money when they are traded as files. All they can do is prevent others from using their videos to generate money, such as putting them on an ad supported website or selling them on DVD. As you know, making copies is protected as fair use and the only legal argument against this is if making copies robs the copyright holder of income from the material. They cannot make this argument with music videos that were released as promotional material. If in the future the record companies offer music videos as paid downloads then maybe they would have some legal leg to stand on, but until then all that those trading videos are doing is giving each other the chance to see what MTV has refused to air.