But here's the rub: VECD licensing is only available as a subscription through Microsoft's Open Value and Select licensing programs. And it's not cheap. Presumably, most VDI implementations will use some form of diskless thin client. The current pricing for this option is about $110 per year (marginally less if you have a level B/C/D Select agreement). Compare that against the roughly $125 you might pay for a perpetual OEM license of Vista Business included in a new PC from Dell or Hewlett-Packard. Granted, that OEM license is significantly less flexible than a VECD license; OEM licenses are nontransferrable and don't include Software Assurance, so you'll have to pay to upgrade to Windows 7 or buy a new Windows license if you change out the PC.
Most enterprise desktop workstations seem to remain in service for about three years before they're replaced. If you purchase a desktop PC with an OEM license for Vista Business, you'll pay around $100 to $125 for the privilege. (It's hard to tell exactly how much because the amount Microsoft charges large business PC OEMs through its System Builder channel isn't public, but I suspect it's somewhere around there.) If you decide to implement VDI and use a thin client to access it, you'll spend about $330 for the same three years.
There's no other way to cut this: It's simply way more expensive to license a Windows desktop OS for a VDI environment than it is to license one for a physical environment. Even if you upgrade to a new major OS revision during those three years by taking advantage of the Software Assurance plan included in VECD, you're still paying more than you would if you did the same thing with a desktop client.
VDI is good for enterprises, but not for Microsoft
So the question is, Why does Microsoft sabotage VDI? The reason is pretty clear: Virtual machines can live forever. By its very nature, virtualization abstracts the hardware from the operating system. You can upgrade your virtualization hosts many times without needing to change your virtualized guests at all. If you're feeling particularly masochistic, you can even run Windows 3.1 on your brand-new Nehalem box. It's no secret that the last desktop operating system upgrade cycle has not gone particularly well for Microsoft. A huge percentage of enterprise customers are still running Windows XP whether or not they actually own Vista licenses. One of the only things saving Microsoft from a huge drop in desktop OS revenue here is the OEM license.
While a business might have decided to run Windows XP for the past seven or eight years without upgrading, the desktop hardware that was originally installed has been replaced one or two times. In most cases, this means Microsoft has sold you one or two more OEM desktop licenses with your new hardware, even if you're not using them to run Vista. If Microsoft's Windows XP licensing agreement had allowed it to be virtualized and VDI had been mature in 2001, you could be running the same full XP license today that you bought then without spending a penny on additional operating system licensing in the meantime. That's obviously not good for Microsoft, and VECD is its answer to prevent this from happening in the future.