You actually get a lot more flexibility in a virtualized environment than you get on a dedicated server because it removes the hardware ties that a traditional dedicated server has.
You can zip up a virtual server and restore it to another virtual server and click run, you cannot do that with a dedicated server because of the hardware dependency.
You can also increase resources on a virtual server on the fly, no need to take a server down to increase ram / disk space.
There are lots of reason to virtualize an infrastructure.