Why is huck surprised by Jim's sad story? What is twains point?

Twain makes several pointed comments about the general attitude towards blacks when Jim discusses his family. Huck comments that he is surprised to find that Jim is almost as concerned about his family as a white person. This prevailing attitude, often invoked to justify breaking up slave families, is something Huck is beginning to overcome. Jim's touching story about his daughter Elizabeth, in which he hits her for not obeying him, is a powerful indication to Huck that Jim is in fact more concerned about his children than Huck's father ever was about him.

Source(s): http://www.gradesaver.com/the-adventures-of-huckleberry-finn/study-guide/section5/