This seems to be an overly simplified take. If Nolan had intended to make it clear that the final scene was indeed reality then he could have just as well shown the totem falling while Cobb walked away. It seems pretty clear that Nolan explicitly intended to leave it up to the viewer to decide what was "real" and what as not. This ambiguity between dream and reality is one of the most important themes in the film - Cobb spends the entire movie preoccupied with keeping track of reality, to the point that one could argue that Cobb's had been incepted to remain obsessed with identifying reality to the same degree that Mal had been incepted to perpetually believe that she was dreaming. When Cobb sees Mal in limbo at the end, she also makes point explicit - pointing out that Cobb has simply chosen to believe that his children "up there" are what is real and that Mal "down there" is not.
The final scene preserves this ambiguity, while underscoring the fact that the obsession with reality is no longer important to Cobb - he is finally at peace with where he is - real or not.
The final scene preserves this ambiguity, while underscoring the fact that the obsession with reality is no longer important to Cobb - he is finally at peace with where he is - real or not.