As I said, it’s not a fundamental limitation, but it is ubiquitous in computing with only a few specialised and obvious exceptions, so breaking it has consequences: you will confuse people. Probably not much, but people don’t try scrolling up from the top of a page, nor left from the left edge.

I also expect that from-scratch layout implementations (the theme of the article) would tend to only scroll in the positive direction, because doing otherwise is somewhat painful, and what kind of weird thing would want negative coordinates anyway? —So they would think.

This is why the CSS text-align behaviour is surprisingly sane. It solves a subtle problem that you would otherwise expect to encounter.