You're right, Jonathan, I was intending to be a bit provocative.  But I do also think there's a genuine issue at stake. Things are very much in flux at present, and this will surely continue for a decade or two at least.  Scholars very much need DOIs as you say, and permanent URLs (PURL) or some similar mechanism.  And although it may seem dangerously ephemeral to refer to a PDF sitting somewhere on the web, the WayBackMachine at Archive.org offers possibility of finding things that have otherwise moved or vanished, long after the fact.  Here's my home page as it was in January 1999, for example.  A nice bit of nostalgia.  And Academia.edu is being very pro-actively archived at the WayBackMachine.  Sometimes there are four snapshots in a single day.

Musings.

Dominik