I agree with Lawrence that a lot of Dimdows boxes are only happy to run one application. However vitualization is more about management. With VMware ESX, for example, you can move the server to a new piece of hardware with no downtime (via the VMotion feature) - So hardware maintenance can be done at anytime with no downtime for the OS and applications.

I don't understand what the big attraction is. As the reported statistics show, it seems to have major appeal among Dimdows users, not so much on Linux. Possibly because Dimdows servers tend to run only one application each, whereas Linux servers are often multirole? Open-source apps are better at staying out of each other's way than closed-source ones?