Care to explain for us who are not eating (regularly) seafood nor parmesan, let alone their combo? Personally I'd find odd to combine seafood with ANY cheese, not sure why parmesan would be any different.
It's one of those myths perpetuated on tv or the internet that Italians will get offended or something like that. There's so much competition in this business that nobody will refuse you, specially when they can add a few euros for a few grams of cheese. And there's also a big chance that the cook/pizzaiolo is not Italian, so these customs are all foreign to him.
One of my friends went to Italy, and they refused to add cheese to his pasta with seafood. Something something a toxic combination.
They gave him the cheese anyway, so it was at his own risk to make the combination.
Disclaimer: I put cheese on every pasta, including the one that has seafood.