the point is: there should be some *easy* way to get/install cabal-install binaries for those who aren't in a situation where haskell platform is appropriate.
I generally regard haskell platform as "for students", "people with enterprise support cycles" and "oh shit, my haskelll install is borked and i need to get things working again right nowwwwww". I understand that certain distros/package managers regard it as a stable substrate (rightfully, cf my remark about support cycles).
But that doesn't preclude people from doing their own setup, and if that is common place (as I believe it is, though i've not done a survey), having binaries at are easy to install is a reasonable goal!
-Carter