Huh... thanks. I have a suspicion I've been pretty much spoiled overseas.
I was working in the Technical department at one of the larger Lufthansa daughter companies, and even before the EU legislation came in there was not a policy of routinely cancelling flights because they weren't 'full enough'.
If there were enough AOGs that the reserves couldn't cover the flights, then the 'underbooked' flights would be the first to go (if possible, etc etc).
In off-peak times (public holidays, christmas etc) they have a different flight plan - but this is usually known in advance (as it's more or less the same every year).
AFAIK they only sell tickets for the available flights.