I agree, kiwicyclo, that point of sale is a nonissue. DOT rules typically apply to flights to/from the US. Occasionally DOT will discuss rules that differ, say, for flights to the US versus from the US. Tarmac delay is a classic example, and this was discussed at length in the rulemaking process.

hoipolloi, my instinct is to start with the black letter of the law and regulation, which tellingly give no support to ANZ's position or to use of point of sale. Let them try to offer some authority that their position is correct. Good luck to them -- I say they cannot do it!