I am truly curious ... why does this matter in the slightest?
It matters to me since we had a very short shut down with the other versions, and since it was no longer the case with 10.8.2, we felt that something was wrong with the OS, and needed fixing.
We like a short shut down so those that do it, would like to leave the computer sooner rather than later, and turn it off to do something else. With 10.8.2, I had to wait until it was shut down so I could turn off the system completely as a safety measure when I leave my home. 20 seconds may not mean much to you, but it does mount up over a short period of time. And no I will never just put my system into a Sleep Mode.
Even Microsofts Windows has a very short shutdown.
If you don't mind it, good for you, but please stop bad mouthing those that do want a better faster system.
6 times now, using the Log Off screen, the time needed is about 3 seconds.
Edited: More activity and now my shut down is around 20 seconds again