As some of you might know Windows 8 has a new feature called Windows 8 fast startup. As the name implies, this allows for a faster startup.
Basically when you use shutdown in Windows 8, the system is never completely shutdown. It basically closes the user sessions and hibernates the kernel session (instead of closing it as with Windows 7). When you us restart in Windows 8, the kernel session will be closed.
It is important to realize this, because some changes to your systems might require a reboot to become active. Even though in the past it was also ok to shut down the system and then start the system again, with Windows 8 you really need to perform a restart.
To manage the Fast Startup feature, check this blog post. Here’s another great blog post that discusses the Fast Startup feature in more detail and also covers Fast Startup in relation to shutdown.exe and PowerShell.