there are soooo many ways to think about the ending. Even more then the "does the top fall or not"
Follow me on this. The whole film is a dream. The street chase, the closing in wall, Saito appearing out of no where to pick Cobb up. A dream makes sense untill you wake up and look back at it. Cobb is so many levels in, and the reality we see is just another level. Now remember the totem, and how no one can touch it. How they then can reproduce it later, and make the dreamer not know if it's a dream or not due to them knowing everything about the totem if they touched it. Why did Cobb let Saito touch the totem at the end? That way, Saito, who is an figment of Cobbs on mind, can reproduce it within another level, and cause Cobb to beleive his level of dream, is reality. That is why the top is spinning, but wobbles when he hugs his kids. He is dreaming, but his dream is turning into his reality.
There are other clues too, to this.
The kids not aging, and wearing the same clothes
Saito calling a "unknown person" to free Cobbs name (to me, name = mind knowledge of the dream)
The whole movie was Cobbs inception of himself. Placing a thought within himself, unknowing