I agree, and I think that's why there hasn't been a huge promotion of Diane's final broadcast across the network. The transition seems very low-key. The network probably wants to maintain the integrity of the World News brand rather than draw attention to who is anchoring and who is not. David has been filling in so often for Diane that some people probably won't even notice for a while that David has taken over, and I'm sure that's intentional on the part of network execs. ABC doesn't want people to stop watching just because it's the end of Diane's era, which I could see being more likely if they played up the fact that she was leaving the desk. It's going to seem very seemless, I would expect. Again, ABC learning from NBC's mistakes.
Also, it would be different if Diane was leaving the network altogether. It helps that she is remaining at ABC and taking on an elite role. It also helps that she likes the person succeeding her. If she didn't, I'd imagine she would demand more attention to her departure.
I don't know how all of that will affect the graphics package if at all, but I think we will for the most part see the same program for the near future. That may change as the show becomes more David's, and as the new EP takes over.