Carmelo didn't have a very good year last year, but had a pretty good playoffs, so I'm a bit surprised. I bet they must think that one of Martin or Nene is going to get injured again, as they have a well balanced roster right now.
That 9th overall pick isn't coming to Chicago though, it would probably stay in Toronto, as they would start rebuilding. (Deng's good for the rebuild because of his young age, and they seemed to have always liked them).
I could definitely see Vinny wanting Carmelo. If you re-sign Ben Gordon, you have a perimeter trio that has the other team peeing their pants, because they know they can't stop them. Maybe sign Rasheed Wallace if Reinsdorf is feeling generous, or otherwise, Mario Austin might be able to be our power forward next year.
I think that trade makes sense for all sides, since Toronto knows they're losing Bosh (the lure of Miami, to play with a better team, with far less taxes will be way too tempting for Bosh to pass up).