So it comes down to memory. If you have extra small desktop VMs (1GB RAM each) and you want to use the Standard Edition of vSphere, you might get away with buying the regular Standard Edition.
But for every other scenario, it looks like vSphere Desktop is the way to go. Therefore I feel pretty good making my official recommendation, “Yes, if you want to run your non-View VDI product on vSphere, you should buy the vSphere Desktop edition.”
TL;DR – buying the VMware View edition of vSphere is cheaper than buying vSphere 5 “standalone” even if you plan on running RDS/XenDesktop instead of View.