"Many changes in Han's character were discussed during story meetings. In coming up with a possible mission for Han, George Lucas fleshed out the character's backstory. Han is an orphan and was raised by Wookiees on their planet. He left, flunke dout of the Space Academy, and then met some kind of Ernest Hemingway character, a very powerful trader in the galaxy who took Han under his wing until they had a falling out. Han swore he'd never talk to him again."
Which goes to show Lucas never likes to throw away and idea, no matter what its merits. As an idea for a backstory I could live with it. As for including it the prequels, well thats just another contrivance that results in making the star wars universe that much smaller.
Which also leads me to another point, how come the prequels have next to no backstory?