OK, well a couple of observations from a non-expert here. I've played this tune a hundred or so times and because I'm basically an ear player I've never had to consider the changes as being weird. I also find the bridge to be the most interesting part of the melody, the (A) section always feeling kinda choppy to me. Anyway, Neely's claim that the original version was written in G is something that no one but Jobim can be certain of and he ain't talking. The song could have originally been written in Db and the arranger for Ribeiro's version could have changed it for that particular recording. I would venture a guess that if hence forth Jobim played it in Db then that's the key he originally wrote it in. All in all it was an interesting video.