If grue-people expect the green emeralds to spontaneously change into blue emeralds, why shouldn't they also expect a simple green-detecting turing machine to spontaneously change into a blue-detecting turing machine and vice versa? Yes, a Turing machine is a mathematical construction; it does not spontaneously change. But they, using "grue" as a basic concept, would expect everything that even remotely depends on colours to change at a certain time, including physical approximations to Turing machines.