Ever see act1 Rogue townie in Cow Level?

[Crystalion]

My personal guess is that it's a deliberate feature intended to keep people talking about the game long after they think they've seen everything.

Yeah, kinda like the stained glass window monsters in act 4.

Somewhat off-topic: it occurs to me you could rush a character, named "Fourth_Ancient" or some such, to act 5 hell while still under clvl 9 (PvP limit, iirc), and fill their inventory with full TP books... such a character could enter Ancients Way and pass on to the Ancient's challenge plateau (interesting build question here: can they do this unassisted, apart from twinks?) in order to do a Pythonesque "none shall pass" "what is your quest?" kind of joke (the crux being that so long as you can cast town portals you can nullify attempts to defeat the ancients).