It's all about the $$$.
VMware have been trying to take the piss with licensing cost for some time IMHO, starting with the introduction of Enterprise Plus and the efforts to get rid of normal Enterprise.
More and more people are starting to have tiered virtual infrastructures now, usually of a vSphere/HyperV ilk. You can't manage this sort of environment from vCenter and this is where the danger is for VMware.
If people start realising that HyperV isn't quite as bad as they've been led to believe, more VM's will go onto the second tier HyperV and the VMware market share will erode.