A few crucial details are missing from this article...

1. There is a significant reduction of metal & plastic in a virtualised environment in comparison to a non-virtualised environment.

2. The virtualised environment requires less human labour, transport costs and fuel usage to set up. The same applies to upgrades (which are no virtual too) and future server deployments.

3. The ability to migrate a virtual server to another country without any physical movement of parts.

In short, less metal, less fuel, and easier management. Also, while I agree that it's unwise to compare a good VM infrastructure with a badly set up datacentre, it's still pretty obvious that a server room that has been designed to cool you virtualisation kit is going to be 'greener' than a larger server room with a larger number of physical servers in it.