I heard it from the AA RTW desk when we were killing time waiting for an airline to respond; I have no interest in buying an LONEx ticket, as DONEx is not that much more and avoids all the hassles of the L ticket (lack of inventory on some routes and limited FF miles). Even ignoring the comfort aspects.

I've run into this before with several different airlines, needing to have inventory in both classes for an upgrade, so it did not seem implausible. I suppose for WT+ all that matters is what BA does, since they are the only ones with this product, and AA's procedures are not relevant. As an aside, is L ever sold out on BA LHR-Australia? I would have thought there is always plenty, given the flight schedules and competition.