I don't know, maybe I'm just a fan of dark, eerie endings, but to me the suggestion seemed to be pretty strong
that Cobb was still dreaming. The top was spinning for an unnaturally long time, and unlike others I saw no sign of it beginning to topple.
Plus the way everyone awoke so easily on the plane, and Cobb sailed through customs... and then he comes home to find his kids waiting for him and playing in the very same place...
It all just seemed a little too smooth and easy for him (especially considering how deep he was, and how long he had been gone), and after I saw the top at the end, I realized why.