The example had nothing to do with the crux of his speech. After blaming the white community, it was a pandering olive leaf.
The Ashley ending was an appeal to the white Edwards supporters.
Obama has used this story many times. (In fact, it was pretty much word for word his MLK Day speech at Ebenezer Baptist. So evidently the anecdote tests well in focus groups.) It always begins with the pointed observation that she's white. IMHO, it's just a maudlin embellishment of the standard "some of my best friends are fill-in-the-blanks." For a guy who claims to decry racial divisions, he sure talks a lot about skin color.