I laugh at everything. I also make myself laugh harder when I think of something that's not really that funny but I keep picturing it in my head and exacerbating the situation. There's not much in life that makes me cry though. Really sad movies will get me, but I guess I just haven't suffered enough because I very rarely feel like crying.
I don't think they are related. Some people just have a really good sense of humor. It's also a coping mechanism. They may find themselves finding humor in even the most desperate situations. I think it's very healthy.
I'm with Puffy, finding the humor in everyday life is healthy. It's like "letting go" of yourself in a safe way. Same with crying, it's a release. It's godd in by book to express your feelings. Maybe it's more of a chick thing, I don't know.