This video in 720p seems to be streaming just fine. I'm on DSL 6 in Kitchener currently and having no issue. I think the problem you may be experiencing here may be that of a network congestion nature.
I'm honestly at a loss to explain why DSL users seem to be affected by this as well.
I know that a few of my friends here on Rogers have had some issue with YouTube at peak hours, but that seems to be an issue that is isolated to the particular POI that they're on and only rears its ugly head around peak hours... Welcome to cable!