See the other post. There is a generic entry about BluRay and SmartTV’s that support 1080p, so I’d assume the WDTV could, too. Maybe somebody with CableVision in the US, or one of the other partners in other countries, can see if you get X-High/HD on a ‘SuperHD’ title. (Hit OPTION while playing to see video quality level.)
It appears that it’s supported. I am currently watching Haywire “superhd”. I clicked option and it does say video: X-high/HD and my provider is cablevision. Picture quality is really good.