I had Logged the Call and found the solution....Actually vSphere 5.0 and 5.1 gives different set of features with the same vSphere Std License. Have a look at below link for options available with vSphere 5.0 and 51.
1-Compare vSphere 5.0 Editions
Compare VMware vSphere Editions for Cloud Computing, Server and Data Center Virtualization
2-Compare vSphere 5.1 Editions
Compare VMware vSphere Editions: Managed Virtualization & Cloud Computing
For a test purpose i used the same Standard edition key on server with 5.1 installed at it worked fine with Storage vMotion Option available :-)