Since I can no longer edit my previous post, I'm gonna add another one here. Your premise is false because your examples ("Member of Parliament") are using a p

Since I can no longer edit my previous post, I'm gonna add another one here. Your premise is false because your examples ("Member of Parliament") are using a preposition. iPod Nano doesn't include a preposition... just a noun or an adjective. The only reason your examples work is because the noun is still being pluralized and the preposition stays the same. The object of the preposition is not the main noun in the sentence or term so it doesn't make sense to pluralize it.