AFAIK there is no "copyright dispute". Whenever talk about the Horde bike being brought back comes up, the legal anxiety that people assume Blizzard has is a Californian law about game prizes. Blizzard advertised that the bike would only be given out to people who were subbed (aka paying $15 a month to play) at the time. If Blizzard were to make the mount available again, then suddenly an argument for a class action lawsuit could be levied against Blizzard because people who only resubbed to get the mount want their $15 back. The American Chopper special was higher profile than other stuff Blizzard has made commonly available like TCG bonus items. This might be the same reason why the MoP legendary cloaks and challenge mode armors haven't been made available again, because Blizzard heavily touted that they were going away and you had to buy the latest expansion and resub to get them while you could.
Paul Jr. answered this. Tank treads were something different, and he felt they were more appropriate for the heavy plate wearers that dominate the Warcraft setting. Having them ride thin wheels into battle would look weird.