Just for grins and giggles I did a distortion control edit to see if or how far the horizon line was out of "level." It is considerably so (about a 1/16 of an inch - 1.5mm at the apex), but I have to agree with Mr. Lim as to it not taking anything away from the image as first presented. The human eye cannot discern that much scope of sight without moving the head from side to side. If we could see an area this vast, would it also be reasonable that we could see the curvature of the earth as well. Here is the edit using only the distortion control feature in "Transform," CS6.
I could have done a post crop as could he, but I think everyone would agree it really isn't worth changing the physics of the human eye, nor the image as shot and presented. For me, this image is almost all about the yummy light.