In actuality, the simplest way to exit the app is to hit the start button. That's it. One tap. Is that idea really so hard to accept? Does it present problems? Is it cumbersome? See, your own argument works for the simplest way, which isn't a task manager. But it's a moot point - it's already a pretty solid rumor that the ability to close from the back stack is coming in WP 8.1.
Um, no. It's not the simplest way. You hit the Windows button and it might take you back to your home screen, but it's still there. Try hitting the back button after you hit the Windows key and you're back to the app. So, no, it doesn't solve it. All it does is hide it from view until you need it again. So if you're in one app and hit the Windows key, you hide it. Go to another app and hit the Windows key, you hide that one. And so on and so forth. You could potentially have X number of apps open, hidden from view. And while this may not eat into your battery life. Anytime you hit the back, it's going to start from the last open app and start working backwards. So, yes, while you may be able to close tabs in IE, try opening multiple different levels of Facebook or One Note. They don't have "tabs" to close. You STILL have to back through everything in order to exit the app.
Furthermore, if I have 4 different apps hidden in the background, hit the back button from the home screen, it goes to the last known open app. Now, if I start backing through that to exit, it doesn't go back to the home screen. It goes to the next open app in line. Also, if you have x number of apps open/hidden and you're at the home screen, try tapping the app list to scroll through something, decide you don't want to open an app and hit your back button expecting to go back to the home screen. Nope. Guess where it takes you? The first known open/hidden app.
So yeah, it's cumbersome.
And "pretty solid rumor" doesn't mean "confirmation". There were plenty of "pretty solid rumors" before GDR2 came out that didn't come to fruition. Regardless, it's opinion. From both sides. Someone felt that it was "needed" and you didn't. But somehow your points were valid and everyone else's is "moot". I just hate when people are so biased.