I wouldn't say I fear any rides - I just wouldn't go on certain rides. Some spinny rides make me feel ill. Not many, but if somebody spins the teacups too fast (Adz.;)) then I feel very crap, and Quantum! at Thorpe Park! Can't stand the ride - last time I went on it, I nearly threw up on Crofty and Wayne mmmm! So I won't go on that again.
It's not a fear as such, it's just a dislike because they make me feel ill, even though I've never actually been sick.
As for other people, well, different things make different people tick. Some people have higher tolerance for these kind of things, I guess. People throwing up after rides DOES happen, and I guess it's not very pleasant for the person who's been sick in public, so I can understand someone being 'scared' of going to AT if they think they can't quite stomach the rides.
I know if AT was a park full of Quantums, I'd be damn scared too and wouldn't go!