Many years ago, I was also told of this ruling, that AMEX (specifically, when I had a card with them then) does not 'encourage' the use of the cc to issue tickets on behalf of other people unless it is for self (obviously) or direct friends/relatives whom you are giving the tickets as gifts. They explained to me that its a way of 'money laundering' where money is exchanged thru a 3rd party. Other cc's do not seem to have this issue.

This was not with amex Canada, but I think the ruling applies.

On another note, tickets issued thru TAs, do not need to show the cc used for ticketing at check-in. Cos the TA guarantees that the use of the card was legitimate. Of note, some *A airlines still require the proof irrespective which was a pain on my last RTW cos the ticket was a gift to me. Specific airlines in question were TG and SA !