Max, A belated thanks for all those e-mail posts. I actually did get an answer from Calfee - from Craig himself (even though I didn't e-mail him directly).
Essentially Craig thinks that the main reason tubes fracture or break is because people don't look after their bikes closely and blemishes turn into something worse. Chipped paint can be addressed by the owner, but gouges would need professional attention (by Calfee).