From the AA.com link

What does this mean:

Tickets Issued on or after March 1, 2005
The maximum weight per checked bag is 50 lbs/23 kgs

Also note the following:

• Baggage checked to London
• Baggage checked to/through/from Europe and Asia
  The maximum weight for each bag checked to/through/from any destination in Europe or Asia is 70lbs/32kgs. American will no longer accept overweight baggage (70-100 lbs.) in these international markets. This policy is in conjunction with the British Airport Authority mandate prohibiting checked baggage into the United Kingdom that weighs over 70lbs/32kgs.
  
  This policy only applies to passengers traveling on American to/through/from any destination in Europe or Asia. If you have baggage weighing over this new limit, please repack or redistribute the weight into other baggage.

I guess that means the max you can check is 70K regardless of co-pay amount - but why this policy when not transiting through the UK?