Now that is a real concern and to a large degree seems to say more about TG than it does about US. I realise your point is well worth it to avoid headaches at the airport, but it's still ridiculous of TG to adopt that stance.
I would vouch your point is not only valid just for award tickets; the same thing would happen if there was a cash ticket.
Finally, it is not as if it is something which cannot be necessarily overriden at the airport. It may take supervisor (sole airline) intervention, but nonetheless. I'm not sure if the "wrong baggage allowance" has implications with respect to payments on tickets, interlining, revenue splitting, load planning etc. which make it necessary for it to be accurate in the first place on the ticket, but in any case someone is clearly at fault if the wrong allowance is issued on the ticket (but again point noted that taking the initiative is better to avoid headaches rather than attempting to deal with it on the spot or after the incident having copped the relevant overweight charges).