The problem is that vert- doesn't just make you loose out on seeing some of the environment, it alters the perceived perspective. It makes things looked zoomed in vs 4:3. E.g. here's our friend Bioshock:
16:9 looks very much zoomed in compared to 4:3, the environment looks a lot closer. With true hor+, one aspect doesn't looked any more zoomed in than other. In the case of hor+, it is purely a matter of some extra environment being visible; you appear to be the same distance from the environemnt, you just see more of it.
I would argue that the level of perceived zoom/perspective has a much, much greater impact on the game experience than simply seeing more or less of environment. If I were a developer and I wanted to keep the vision of my game as consistant as possible, the perspective/perceived zoom would be way more important to me than a couple extra virtual feet of scenery being visible at the sides.
I mean assume that 2K is being honest that they chose the really tiny FOV for widescreen to give the game a crampt/claustrophobic feeling aren't they then compromising the experience for 4:3 players by not reducing the FOV by an appropriate amount for them? Doesn't 4:3 seem less crampt compare to widescreen? Definitely. The problem is that the "intended" FOV is just
too crampt, to the point where it's so zoomed it seems unnatural. 75 degrees is already smaller than most games at 4:3, so at 16:9 it's really bad.
Anyway point is that hor+ ensures the most consistent play experience for all aspect ratios.