What you're missing is that if you were designing an OS from scratch today with absolutely no legacy cruft whatsoever, even if you went with a "desktop" style paradigm with overlapping windows etc, you still wouldn't design it in a way that requires users to "open" or "close" applications. It's a throwback concept to a more simplistic design age. It just doesn't make sense to burden the user with that kind of manual resource management when the OS is far more capable at doing it - that way you let the user focus more time on the thing they are actually trying to accomplish.
No you're missing the point. The Windows Store app "task bar" cannot be considered like the W7/W8 desktop taskbar because it doesn't show all open apps and living with the idea that you don't need you close apps (good or bad) hammers that idea home. That was it. Simple. Instead you choose to whip up some apology for the over simplified Windows Store app environment.