Here's an official video/ad that highlights some of the ways people will use Windows 8 in Microsoft's eyes.
http://windows.microsoft.com/en-US/windows-8/release-preview
http://windows.microsoft.com/en-US/windows-8/release-preview
it looked like that kid wasnt really doing that stuff on his screen.
Disclaimer: MSFT employee
I feel that doing all of the touch gestures with a mouse is a bit much, especially pull down from top to close.
I still havent seen a better solution to multitasking/app management than webos.
I doubt that discoverability is going to be a major issue, though, because edge swiping will get a lot of exposure through ads, and through any in-store use as well. It's such core functionality that every Windows 8 touch user will have to learn it in the first 2 minutes. If nothing else, they'll turn to the person next to them and say "how do I get back to the start screen"?
As for closing metro apps, there's not really any need in general. Just go back to the start screen. You can also close apps in the app switcher on the left, but the current app isn't in there if I recall correctly, and it's still not necessary in general.