Personally no I don't think you are being unreasonable. I know other manufacturers (such as BMW) do replace them under the original warranty although on a case by case basis. Diamond cut finishes to alloys do fail and I think they are the worst for then corroding as water gets under the top coat. I am probably not explaining the process very well but in essence that is what happens. As soon as any mark is made then water ingress will follow and they end up a milky/cloudy finish. There is only so many times an alloy can be refinished when diamond cut as well.