Earlier quoted context omitted.
It's mainly to keep everything (where everything == files, REPL, docs, etc.) in a single window, which I can then throw full-screen and have absolutely nothing but my work in front of me. I'm sure one could use ST2 (or any other GUI app) on Linux with a tiling WM like xmonad and achieve a similar workflow, but there doesn't seem to be a way to achieve this on OSX that doesn't involve ugly/unstable hacks.
You know, in theory it'd be possible to do that within Sublime but I'm not sure if that's veering towards the emacs approach of ALL THE THINGS. I'd have to try it but I think you can probably use PyQt to grab WebKit and make a package to display HTML docs within Sublime
[1] The other is it's absolute refusal to "fit in" on whatever platform it's on. Fits with the kitchen-sink approach: why interop with [program X] when you can just build it in?