Since Disney is so dedicated to keeping up the illusion, I wonder if that may be part of the reason for getting rid of the skyway. When you're up in those cars, looking down on the roofs of the buildings, probably with gum and stuff on them, that probably doesn't help to maintain the magical illusion that they're trying to portray. Unless, of course, they took the skyway into account when doing the roofs of the buildings, and made sure that they fit into the illusion as well. But I'm sure they had to spend alot of time scraping gum off of the rooftops.