I just found the time to watch Trevor Dickinson's AmiWest 2011 presentation and there I heard him say:
"There were 20 improvement changes from revision 1 to revision 2. Most of them were minor things [...] but there were a few major changes like changing the onboard Ethernet to use the PHY from PA Semi [...] and also changing the audio circuits."
...and it has the following on a slide:
"Revision 2.1 design to correct several issues:- [...] Incorrect audio connector pinout Resistor changes to the Ethernet PHY [...]"
