I have noticed that most non US airlines have different rules for checked luggage than they normally have when the itinerary includes travel to/from/within the US (& it's territories), Canada and South America.

Does anyone know why this is so?

Is it a legislative requirement, an IATA rule?

For example, look at these links to Ailine Baggage rules[Non US Y/J/F allowances]:

• Qantas[20/30/40Kg]
• British Airways[1/2/3Pcs]
• Singapore Airlines[20/30/40Kg]
• Lufthansa[20/30/40Kg]