Hacker News does everything correctly to _functionally_ indicate that the area is scrollable. It does absolutely nothing to _visually_ indicate this. And the CSS spec does not require that the browser visually display scrollbars.

So no, Hacker News is in the wrong here. They're relying on the assumption that the user is using a browser that renders scrollbars, and providing a sub-par experience for any browser that does not. This is somewhat analogous to a site that only renders correctly in IE.