"One binary" is a bit optimistic; even if you never do anything fancy with fonts, you'll want bibtex. And makeindex, if you're writing a large work. PSTricks does not work with PDFLaTeX (Tikz is arguably better than PSTricks, but PSTricks won't be dead anytime soon). XeLaTeX is required to use system fonts easily.
And that's before getting into anything truly gross.
I am running a TeX distribution with only one binary. And with bibliography and index: these could be done with the Lua part of LuaTeX. True about the others.
Indeed, Norman Ramsey essentially reimplemented Bibtex in Lua: look at bibtex.lua.in in his Nbibtex; tarball avilable from http://www.cs.tufts.edu/~nr/nbibtex/
And that's before getting into anything truly gross.