It's just a strange and completely non-scientific theory I have, but maybe cats are more aware of the dangers of a particular environment than we give them credit for. I've had the same experience as Jen--my Katie, in particular, spent a long time outside and she wants no part of it now. My neighborhood is not at all cat-friendly (busy intersection, cars always speeding up the street), and I think they know they're better off inside on the sofa. But where the outdoors doesn't "feel" so threatening, I would imagine that cats would prefer to get out and enjoy it.