This is actually a point where GIMP wins. You can, albeit with a little effort, perform operations like curves in HSV-land, and peel out the resulting values (or whatever). Effectively.
This is basically a problem with every tool, though. I guess you can argue that curves is nastier than other tools, but they all do a bunch of stuff to a picture, while essentially advertising one of the effects as 'the thing they do'. It's kind of an inevitable consequence of the way the universe works.
Jay's post didn't go in to any of this, though. It was just some ranting, backed up with some vague remarks about light and some incorrect remarks about Ansel Adams.