On last nights episode of Only Connect why was it perfectly fine for them to spoil GoT & tell everybody that it was Tyrion who shot his father Tywin as he sat on the shitter but it was somehow beyond the pale to reveal the killer of Moaning Myrtle from HP? (It was the Basilisk from the Chamber of Secrets) 

Are HP fans some sort of rabid group of monsters such that VC fears for her life should she spoil anything for them?