Are the lines between the NAS and the SAN becoming blurred?

Yes that difference certainly gets blurred. Like the DDP more and more NAS solutions also require installing a driver on the desktop. Of course there are many companies offering open source NAS solutions with XFS, ZFS, ext2/3 FS etc. under the hood. There is nothing wrong with that.
But if I were an owner of lets say a post production company with ten seats I would go for one of the hybrid DDP solutions because it give me project caching within a single file system and I would not have to worry too much about overloading the system: best of both worls so to speak. No matter how big the installation grows with DDP there is always a single file file system no matter what you add on.
With NAS you quickly come into the name space world.