Wow, that's a fantastic post Richard!
"Your bad edges are not limited to the keyed edge, they are everywhere. These are compression and/or resizing artifacts. The most likely cause is that the files you uploaded to Vimeo were not the right format or size and Vimeo resized and re-compressed them. The other thing that happens when you send Vimeo and YouTube a file is that their site starts building low rez copies of your file so they can stream at different resolutions. The low rez copy is the first one delivered. The higher rez copies take longer. Does your file look as bad after an hour or so with HD turned on in the Vimeo player?"
That's exactly what I was wondering.