My understanding of the difference between PPPoA and PPPoE is that the former uses ATM and the latter Ethernet. Therefore if you have a DSL connection through your normal analogue phone line, you use PPPoA. If you've got a cable connection, you use PPPoE.
For many years this understanding has fed and clothed the kids and kept the wife in shoes.
However, the other day a friend asked if I could help him setup a wireless router at home on his DSL line - he's got an AOL account. "Yes, no problem" I said. But couldn't get it to work.
After a call to AOL they told me that I needed to be using PPPoE not PPPoA. After much protestation on my part that PPPoE wouldn't work, I grudgingly agreed to try it. And what do you know - it worked.
How can that be?