I think a lot of it has more to do with the actual power buttons seen on various types of cases there. On a premade system the sensitivity is higher for the light touch while if you work with a gaming case you have to press a little harder resulting in a more sustained contact.
In Vista you don't have the option for setting that to restart but instead have to go down the list in the dropdown menu there.
A switch is a switch. It's a push-button switch, not a toggle switch or anything like that (sensitivity would be more like a pot vs a switch).
Like Mak said, it depends on what you set it to do in the Power Options (XP, Vista, 7, doesn't matter) when you press the power button. Simply pressing (push in, let go), you can set it to either Do Nothing, prompt, hibernate, or shut down. Holding it for 4-5 seconds however, is a force shut down. You may be thinking of the reset switch, eyeCpc. And like CrazeD said, it depends on what you set it to in the BIOS. I have mine set to wait 4 seconds, but I can also set it to Instant Off when I press the power button.
The type of button in the case doesn't matter, is its just a pushbutton switch in all cases (forget the actual term for the switch...too late for me to be thinking right now).