That's a fair point, I think one big difference here is that we need to replace the hosts anyway (storage/hosts are part of the same lease) so once you factor in that you're paying a certain amount for the spindles regardless of what the storage layer is, it's not so bad, seems to run around £6k for 4x10tb VSA licenses.
That's much easier to replace if our needs change in a years time than if I stuck in £100k of Netapp/EMC.