Theoretically, you have a point. Practically, you are reading this comment on a website that not only does exactly this, but refreshes the entire page (rather than a small block of HTML, intercooler-style). The performance benefits are evident.
That said, it’s a very simple and effective design. It’s an excellent program. But it’s not a fair comparison against other applications which, for one reason or another, need significantly more advanced state.
I mean, this website only loads a very small amount of text and has barely any user state besides a list of comments and posts. I would hope that it loads quickly.