Re: Someone please explain why....
So it's completely possible that Cobb has merely accepted a dream as his ultimate reality by the film's end (while being in a vegetable state in reality).
I don't think CObb cared about the totem at the end, which is why he left it without seeing the outcome of the spin. He has accepted a reality, which is the reality to him, regardless of whether it's seen as a dream to anyone else.
Alan Moore on comics:
They've lost a lot of their original innocence, and they can't get that back. And, they're stuck, it seems, in this kind of depressive ghetto of grimness and psychosis. I'm not too proud of being the author of that regrettable trend.