I agree. In the dreams, it spins indefinitely, or at least it's supposed to according to spoken dialog. Cobb also spins it once or twice in definitive reality where it falls. Of course, there's also the totem aspect of it. They make special mention to say that no one else is allowed to touch it. Since no one else knows it's specific weight, the angles, etc etc, that make it unique then they know it's theirs...it's "real".
From what I recall, two other people have touched this totem. It was his wife's, but we only see it in her locked box in limbo. Also, when he goes to save Saito...old Saito's men bring it to him and he spins it. Now, if this was indeed the same top as his late wife's, she has touched it but she's dead so I'd think that's moot. She also dominates his subconscious though, who knows how much power that lends. Also, old Saito touches it, but only in limbo. Does this affect the totem?
It definitely feels like a purposeful ambiguous ending. If Nolan wanted to push it being a dream, he could have cut the scene before any doubt enters the mind. Or he could have shown it fall. The first sound of a wobble is meant to send the viewer out reviewing the movie and heck, even their view of reality. This could all be a dream after all...it definitely feels real. Ending this type of a movie with a definitive statement on that issue would feel cheap and "Hollywood happy", where you don't have to think too much.