Originally Posted by http://screenrant.com/inception-spoilers-discussion-kofi-68330/3/
Throughout the film, Cobb continues to obsess about spinning the top and verifying reality – however, at the end of movie, he spins the top and walks away from it before he can verify if it stops spinning or not. His kids come running in and Cobb couldn’t care less about about the top or “true reality” or extraction/inception anymore. He just wants to be with his children, in whatever place he can be with them. That emotional connection and desire is “reality” enough for him.
UPDATE: Christopher Nolan himself has endorsed our interpretation of Inception‘s ending.