What makes up the extra 7-9 points. What is lacking? How many beers out there that have a 93 rating?
The two main weak points of it in my opinion are that it isn't as thick as I would prefer (not that it is thin but I expected a barrel aged stout to be more viscous) and that I feel that the bourbon flavor wasn't as potent as I would prefer. I also felt that the flavors weren't well integrated. I view Goose Island's Bourbon County Stout as a better bourbon barrel aged stout as it was more viscous and had a stronger (though not overwhelming) bourbon barrel flavor and smell.
The positive is that all of those things might (and probably will) change with aging. The 93 is a rating as of now, now what it could be in a year or two.
In some ways it reminds me of Deschutes The Abyss (not in flavor though) in that I find The Abyss to be a great beer when it is first released but with a few years of aging it is an amazing beer and I hope that KBS follows that trajectory.
The honest truth is that I don't know exactly how many beers have scored a 93 or higher but off the top of my head I would say, Pliny The Elder, Stone Enjoy By, Most of Russian River's sours, Goose Island Bourbon County Stout, Rochefort 10, St. Bernardus Abt. 12, Lagunitas Sucks, Alpine's Pure Hoppiness, Exponential Hoppiness, Nelson (and probably Duet as well), Stone RuinTen, Lost Abbey Deliverance, Ballast Point Sculpin, Weihenstephaner Hefeweissbier, Societe the Pupil, Green Flash Palate Wrecker, Oskar Blues Ten Fidy.
Beers that I view as similar rating wise (not that the taste the same) would be things such as Ballast Point Victory at Sea, Deschutes The Abyss (right after release), Gulden Draak, Cuvée Van De Keizer Blue (right after release, this is an amazing beer after 2+ years of aging), Ayinger Celebrator, Russian River Blind Pig IPA, and Clown Shoes Extremely Angry Beast etc.
Two caveats, first comparing between styles is somewhat difficult and inexact, and secondly, I think that KBS might improve with age.