It make sense that Apple will offer a wide range of "personal" choices, including other metals. Most jewelers offer 10kt, 14kt, 18kt... I can see Apple offering Pt and perhaps other precious metals too.
Gruber's write up about the price and cost of the metal bands in interesting too (daringfireball). Not sure if Apple has a patent on their band attachment technology to prohibit third parties from making their own bands.