I'm afraid that is true as it may involve copyrights, trademarks and stuff like that which is already in place. However, reconsidering the decision -- if possible -- would make a very good first example of how this company is listening to the already established customer base of this fine product ;)
My personal opinion: if UBB stands for "Ultimate Bulletin Board", then, "UBBThreads" would translate to "Ultimate Bulletin Board Threads" which doesn't make sense and has nothing to do with UBB as they are completely different products. Not only is this (IMHO) misleading but it has the potential to make some people jumpy (from what I've seen here and from some who used said software and shared their feelings in this matter with me).
Now bussiness is bussines so if this rename thing is unavoidable from a legal standpoint, fine. As I said earlier, I will support Rick as much as I can, unless I come to the conclusion that w3t does not serve the purpose for which was created (or if you deny me access to the community -- whichever comes first).