I don't know about you, but I find topic and focus to be a very confusing mess. I waded through Lambrecht, hoping for clarification and came out even more confused! I've been reading various linguistics introductions and dissertations. They all stumble around when they discuss "aboutness." Do a quick Internet search on linguistics and "aboutness" and tell me in a coherent paragraph what in the world it means!
That being said, I think I am beginning to see, even if dimly and through a fog, what in the world they are talking about. Maybe someday I'll be able to explain it so that someone else can understand it. But not yet...