vSphere web access - It is been given an alternative to the ends used to perform administration task on the VM's without using vSphere Client, Not all vSphere administrator tasks were available on web access
From vSphere 4.1 Document
Note
vSphere 4.1 is the last product release for vSphere Web Access. As a best practice, VMware recommends that you use the vSphere Client, which contains all the functionality of Web Access. Because vSphere Web Access is no longer being developed, support for this product is provided on a best effort basis.
vSphere web Client - This is alternative to the vSphere Client and all tasks can be performed on web client. vSphere web client was released from vSphere 5.0 and going forward only web client will be available for the administrators to manage the vSphere Infrastructure.