I don't think they've thought this through very well.
What I think that they mean by this is that they want seamless integration of state shared between environments. That is, they want to have access to all the same information, applications and capabilities regardless of the device that they are currently using.
That is approximately what Google is trying to do with the Google Apps system: stop using your calendar on your phone, start using it on your desktop, just with a bigger screen and better keyboard. It might not be that hard to build a secure state-sharing system to make every phone application migrate to your desktop when it's in range.
The phone itself, though, has the affordances of an always-carried pocket device. Every time you stand up to go consult with a colleague, use the bathroom or stretch your legs, you expect the phone to be with you. Even if you only need to unplug one cable, that's still a significant inconvenience, and a major strain on the connector. Short range wireless connections might be enough in the future, but can't possiblly be as performant as a direct cable.