Just to state the obvious but all fizzbuzz really tests for is whether someone is familiar with the modulo operator or not. Arguably any good programmer should know about it, but I think it's not a very comprehensive check on the knowledge of any one particular individual. Suppose for instance, that the only bit of code someone has ever written was something which required them to get very familiar with the modulo operator, but virtually nothing else. They could pass fizzbuzz, but not much else.

Note: The author of the 'non-programming programmer post' saw took my comment down when I had posted it there (which is why I posted it here). Guess there's no knocking of the fizzbuzz test allowed... :p