Presumably the original contract here was subject to the laws of England and Wales, and the parties to it were clearly UK-based, which make it less surprising that the court ruled the way it did. 

Although evidently a blow to Duran Duran, it is important to remember that contracts (and particularly choice of law provisions) will carry significant weight in a court since a contract sets out the legal agreement reached between its parties, as well as the relevant law to which that agreement is subject. 

If the band had been allowed to claim that laws in another jurisdiction (here the US) could circumvent the terms of the contract then that could create significant uncertainty for this and numerous other agreements and undermine concepts of legal and contractual certainty. 

Although an unfortunate result for Duran Duran, hopefully this case will encourage other acts to ensure their rights are properly protected early in their career to avoid finding themselves in a similar situation.