QF used to have (don't know the current rules, only 5-10 years ago) very strict weight limits on all domestic flights. I remember being yelled at near the security checks (there was no scale, they were just guessing that mine weighed too much and I'm sure it did) but still allowed to carry on normal US amounts in their business class. I also recall even stricter weight limits for all luggage (less than 20 kg total for carry on items and checked bags) for some of their tiny aircraft serving smaller airports.