"breaks too much stuff" over 80.
This is the same FOV cap as in multiplayer, but it can be adjusted in single player up to 80. Many complain that FOV options are too narrow (literally) with some studios releasing patches.
The field of vision determines how much you can see on the screen and 80 is considered rather low and certainly not realistic to what a human actually sees when looking.
"It is the same cap as Blackops mp, but now you can adjust fov in sp and zm too. > 80 breaks too much stuff so we had to cap it," Treyarch's pcdev. The studio is unlikely to ever increase this cap because of the technical hurdles it would have to overcome which would require significant time to redesign UI elements, animations and such.
For some the FOV issue is just a mild irritation to do with preference but for others it can actually cause discomfort and nausea because of the unnatural field of vision. With today's widescreen monsters plugged into our PCs and consoles, it's getting to be a little embarrassing to have these narrow FOVs forced onto blockbuster franchises.
Call of Duty: Black Ops 2 releases on Xbox 360, PS3 and PC November 13th.