As smart as the Hacker News set may be, most people are not experts in the field and could do with a little context.
Also, Aaronson's a well-known computer scientist, so this helps establish that the result's both credible and important in the eyes of people who may not (forgive me) all be qualified to judge the paper on its merits.
edit: Okay, rereading this article I recovered an insight that leads to a truer reason Aaronson's worth linking to. It is not that he's a famous professor (he is) so much that he is, in general, a great expositor. Read that big-number article and tell me he's not.
Also, Aaronson's a well-known computer scientist, so this helps establish that the result's both credible and important in the eyes of people who may not (forgive me) all be qualified to judge the paper on its merits.