because customers are starting to switch to Hyper-V, the Windows hypervisor-based virtualisation system which comes bundled in with Windows Server 2012, rather than paying extra for VMware.
This is probably one of the most important points... I haven't tried the latest version of Hyper-V, but certainly on previous versions VMWare was markedly superior. However when it comes to a price comparison, free (convenient) and separately paid for are very different choices and while as soon as you start expanding your requirements Hyper-V prices do stack up, it's the initial hurdle that's one that can be hard to beat. MS is just front loading convenience to get users used to Hyper-V as a form of lock in for later and it's something that VMWare would find hard to counter in a similar fashion without losing a large proportion of their income.