Though sometimes I refer to Graham as PG when commenting on Hacker News, I consciously try not to because I've not met him and I try to separate the feeling of intimacy that stems from having constructed a virtual Paul Graham from the actual person I have not met. Within the context of Y Combinator it probably makes a lot of sense, but on Hacker News, it draws a bit of a circle around insiders and outsiders. I don't think it's intentional, but I don't think it's particularly constructive either.

Not knowing what "PG" means can be taken at face value. People can still write amazing comments and submit great news items without knowing or caring who "PG" signifies.

I think you make a fair point. Hacker News is constantly growing and Paul Graham has been less active for many months and since Sam Altman became the public face of Y Combinator, Graham has been less visible and the ability to recognize all the Ycombinator partners by Hacker News user name isn't particularly valuable.