I think that is also possible that Cob is in someone else's dream. Possibly Mal's, his dad's, or Saito's. The reason for this is because even in "reality" there are things that are defiantly dream like. First off after all the time that has passed between when Cob leaves his children and when he get back to them at the end, (1 to 2 years) they do not age.
Aslo Saito tells Cob to "take a leap of faith" which is the same thing Mal said to him before she killed herself.
The wedding ring theory claims to dismiss all of this. It states that in reality Cob is not wearing a ring, but whenever he is in a dream he has a ring on.
This is because his subconscious has not realized Mal's death. But if you believe that he is in a dream the whole time and he doesn't know it, he only has the ring on when he thinks he is dreaming.
Stay thirsty my friends.