I'm a fedora (19/ x86-64) user. When I power off the system, it always takes about 3 to 4 seconds to shut down. But whenever I reboot the system, it takes the system much longer (about 30 seconds or more) to power off (and then it starts again).
I suppose that the process of a power off, till the point of termination of the operating system and powering off, is exactly equivalent to a reboot and the differences start after that point, where in the case of a reboot, system boots again. So why a reboot takes longer to power off the system than a power off?