Well yeah, but an ending like this is kind of MEANT to hit you in the gut, and be a bit haunting and tragic.
To me, that's much more powerful and thought-provoking than if he had simply gone off and lived happily ever after with his kids in the real world.
This will probably be one of those things where it'll just be a simple disagreement, but...
I don't think the film earns a "punch in the gut" ending. I feel the tone of the film requires a denouement. For all the talk of Inception being a "mindfuck" film, I didn't think it was at all. I thought everything in the film was clearly laid out, everything flowed perfectly smoothly, and at no point did I feel confused or wonder what was going on or feel like I was being led to believe something that wasn't genuine and earnest. Like I said, at the end of the film, I snickered at the cut to black, but felt the only possible resolution was that Cobb was back to reality, because that's what felt right to me. It wasn't until afterwards I started considering the thought that it might all be a dream, and thought if it was, at least it had a pretty fight scene and I was entertained. I felt the film was pretty standard in the way it flowed and in the way it told its story and that it was pretty conventional filmmaking. What makes it stand out is its exceptional ideas and plot contrivances to tell an extremely literate and intelligent story.
I don't think a film that is as genuine and earnest and conventional as Inception earns a "gut punch" ending. For that to work, I feel you have to work up to it. I didn't feel Nolan was, and feel like the cut to black was an unearned "kick."