I think he has a point about building a national squad around an established team. The Spanish team instantly took on a lot of Barca's character due to the men controlling midfield.
The problem for England is this: United has a lot of English players but their quality is concentrated in foreign bodies. Apart from Rooney, the most important United players tend to be Vidic, Nani, Valencia, Berbatov, Evra and Cheetos. Young is in the picture now, but England just wouldn't be able to bring the same quality to bear, especially in attack. in place of these guys, you have Downing, Defoe, Crouch.
Finally, you would lose the coach. United's current style just isn't akin to anything I've seen Capello do at club level. It would be hard to imagine such a fluid offense under him.