If you manage the desktops properly, and have appropriate policies in place, data can be stored centrally even if the OS and apps are local. Likewise, OS and app deployment etc can become solved problems (App-V has its place, but tends to only help with the apps that are easy enough to deploy by other means - try it with ArcGIS sometime).
You then have the benefits of interchangeable client devices, but also have the benefits of local processing power (including local GPU if appropriate), local storage of the app itself, and less dependence on network bandwidth and latency. A room full of users all starting ProEngineer at the same time only thrash the local disks in each machine, and don't thrash the network, the central storage, or any central VDI servers. Laptop users can use offline files and the like. Other routes (citrix, etc) can be provided for remote users to access their apps and data. (This is a far more plausible home-working scenario than VDI).
At which point, just what is the problem that VDI is trying to solve? The overheads, costs and risks are huge, but where's the benefit? Seems to me the benefit is to those people trying to sell new kit, not to the IT admins, or to the users of the services being provided.