I think that there are two problems going on at the same time, and it's clouding the issue. On the issue of IP rights, I don't think that there's any question that Creative has the law on their side.
As a separate issue, if I understand correctly, Creative has sold to people sound cards that are promised to have certain features. These operate OK in XP, but are locked out when the customers upgrade to Vista. Depending on the nature of the advertising that promised those features, the affected customers may have legitimate complaint about fraud on Creative's part.
The fact that Creative (may have) committed fraud does not invalidate their IP rights.
On the other hand, legalities and ethics are two different things. Creative seems to be within their legal rights, but (again, AIUI) their behavior seems strongly unethical. This is ample reason to refuse to use their products. But it's not going to keep the guy who modded the drivers out of court.