One Story?

I was recently told that most, if not all great literary works follow the same basic story line. While I can not tell you what that story line is, I can tell you that I have noticed this same pattern in many places other than great literary novels. Authors tend to write the same story line over and over again whether it is love lost then found or an adventure that ends just as another begins (which then leads to yet another story). I have recently become obsessed with books by Sarah Dessen. While these books are not quite up to par with other works such as Great Expectations or All The King's Men, they still are considered good teen books. I have noticed that lately, all of her books are following a similar story line. Some of this is on purpose but some of it is simply the style of the writer. She writes about improbable teenage romance. For example, the rich girl falls in love with the boy that works for a catering business and has a juvenile record, or the girl falls in love with the guy who has long hair and ends up being an abusive boyfriend, or most recently, the girl who is going though a rough parental divorce falls in love with a smart above average IQ guy that also has a record for underage drinking. I find a few patterns in this, almost all the guys she writes about have some sort of illegal problem or some sort of bad experience with the law. Also, the girls tend to have some sort of family problem whether it is a divorce or the death of a parent or having to visit a parent that they don't like.
Another non-literary example of a similar story line is Disney movies! As has been long since noticed, every princess has a family problem or the death of a parent. One of the only exceptions to this rule is Sleeping Beauty but in that case the parents are frozen so it is like being dead. Another exception is the recent movie, Tangled. However, in that case the parents are not really involved in the story and the girl has no idea who her  real parents all. So in general, Disney movies have parental problems. This trend has long since been noticed and accounted for but that is what makes a Disney movie so great. The main character goes through a growing-up process that in the end leads to their happiness.
I believe that there are two reasons for these patterns. One which is more obvious is that the author or creator simply is best as creating one kind of story. That one story line sells well so the author writes more and more of it. The other reason is that it makes a great story. This is what Disney does. Disney creates stories that have parental problems because that way they can create a good fairy tale that has all the morals of Disney. Disney teaches kids to have an innate sense of right and wrong because their characters show that inborn sense. Despite the fact that the characters have lost family or don't know their family, they grow up being good productive citizens of the Disney world.