I too received the letter today and the OP is correct, this represents a massive downgrading of travel insurance and travel inconvenience cover including delayed/lost luggage. Amex now insist you pay for travel using a range of specified (note not all) Amex cards. I cannot believe that the cost of this insurance has, first, risen so much, and second that income they receive from travel costs booked on the card will in any way compensate them. In essence the 'use Amex' rule is an attempt to reduce the number of claims, as of course is the loss 70+ medical cover.
All this was a major benefit of the Platinum Charge Card for me, especially luggage delay claims. The changes bring it into line with insurance provided free or at lower cost by other card providers when travel is booked on their card and I will seriously consider cancelling my Amex card as a result.
This is very bad news indeed.
bmifly
