Not that I don't think Sydney is bonza, and is on our list of things to do ( shame we can't drive there it would be a definite road trip destination) but,
the surveys seems to be a marketing gurus measure of how random people around the world perceive the city. It's famous enough for people to have heard of it, and vaguely good stuff like it's in Autralia where it's sunny and they drink beer, but not infamous enough that people have heard bad stuff about it, if there is anything, also Hollywood doesn't make movies about it being crap.
I would like to say "flamin' galah" in no particular direction what so ever