Cobb accepted "the reality of the situation"? That's fine, I guess. But it is a bit of an empty ending for me, because Nolan actually made characters that we care about (or at least, I did). To just say "well, he's accepted it as real" seems hollow. Because if it's not real, he'll figure that out soon enough, and is back where he started. But it's definitely one interpretation.
I agree with that lecture guy, that Cobb does not have a totem. The top is Mal's totem. It doesn't tell you much of anything really. It is a distraction in that regard. However, we learn that the top also represents some dark secret that Mal never revealed. The secret could simply be that she wanted to forget she was dreaming, but I can't quite recall if it was stated that way explicitly in the movie. If it is spelled out that way, I'd have to re-watch again to pick up the exact line regarding it, and how it is presented.
I read a number of different interpretations, but these are the ones I found intriguing, other than the more obvious ones. I'm not necessarily subscribing to any of these, just throwing them out there for your reading pleasure.
1) One interpretation would say that when Saito caught them trying to break into his head in a dream, he thwarted them by tricking them that he had actually hired them to do this other, more complex job instead, and they were in a dream the entire time after that. The "inception" in this scenario would be that Saito convinced Cobb that this last job would get him back home, and then, that he did get back home. This theory is also bolstered by several weird events involving Saito. I know he's powerful, but he can clear Cobb with a single phone call? He can buy out first class of a specific 747 in a heartbeat with no issues? The son of his biggest competitor walks right past him without recognizing him? He conveniently interrupts Cobb when he is trying to spin his top in the bathroom. He also conveniently saves Cobb in that chase scene in Mombasa. It has been noted many times how that chase scene has a lot of dream-like elements (the maze, the narrow passage Cobb almost gets stuck in, etc).
2) The entire movie is a dream, and a ruse to help Cobb extinguish his demons. In this scenario, Miles (Michael Caine - the father-in-law professor) would be the "architect" of the dream - the only one outside his circle of cohorts that is aware of what he is doing. The idea here would be that Miles is tricking Cobb into thinking he is in reality until he gets his personal demons sorted out. Presumably Mal is back in reality waiting for him to return when he gets his issues behind him. Even in this case, though, it doesn't appear he ever makes it quite back to that "reality" in the end, but maybe a single level from it.
3) There is the scene where they go and find Yusuf with all the potions. Cobb tries one of them out. One interpretation is that from that point on, everything is a dream. I haven't explored this one as much, but after that point Cobb never gets to spin the top again, until the very end. This scenario is kind of intriguing but makes the least sense because Yusuf has no real motives. Unless of course I missed something subtle with Yusuf, which is entirely possible.