Favourable licensing in that Hyper-V server is free, and Hyper-V as a role has no additional cost on top of a Windows Server license. Add to that the free VMs available (IIRC 2 on Standard, Unlimited on Datacenter) and if you are a Microsoft shop it makes a lot of sense.
The learning curve, I was speaking from my own experience of how quickly you can get a VM up and running. I've had all manner of fun myself with iSCSI, MPIO and 3rd party software not playing nicely together.
Both products have their foibles, my point was that Hyper-V has closed a lot of the gaps between itself and VMware in the last few years.