He encontrado este artículo en TechTarget, de Brien Posey, que me ha parecido muy clarificador. Os lo adjunto:
What is the difference between VDI vs. Terminal Services?There are many differences between VDI vs. Terminal Services, but they can all be summed up as differences between operating systems and how sessions are handled.
Windows Terminal Services -- now called Remote Desktop Services (RDS) in Windows Server 2008 and up -- was Microsoft's early attempt at creating an environment where users were not dependent on the local desktop. Users connect to a session by way of a Remote Desktop Protocol (RDP)-based client, the same way they do in virtual desktop infrastructure (VDI). The similarities between the two environments end there, however.
In a Terminal Services environment, the user sessions are based on Windows Server instances. As such, the sessions become the isolation boundary between one user and another. Users actually work within a Windows Server operating system rather than a desktop operating system, such as Windows 7. In some cases, this can be problematic, because not all applications will run properly (or at all) on a Windows Server OS.
VDI works differently. You can base VDI images on Windows Server if you want to, but that's not the only component at work. Instead, users connect to a connection broker that links the user session to a virtual machine running on top of a hypervisor. This virtual machine typically runs a Windows desktop operating system, such as Windows 7 or 8.
VDI environments tend to be more complex than Terminal Services environments. Despite the added complexity, many administrators prefer VDI to Terminal Services because VDI allows the user to work in a familiar desktop OS, and because VDI tends to be a less susceptible to application compatibility issues.