> As to why pg can't use normal pagination instead of user-specific state, I dunno ...

I can think of one reason:

* A user loads the front page.

* By the time the user clicks "More" at the bottom, page 1, and all subsequent pages, have been updated with new content.

* So the server can't provide the old page 2 to a user who just saw the old page 1, for the reason that neither of the original pages even exists any more.

* To avoid confusing the reader, instead of providing an out-of-sync page 2, the server instead shows a "expired link" message.