If you click through from that page to the actual terms you will read:
Extra Membership RewardsŪ points at amextravel.com
I read this to mean that we can no longer stack the PRG 3X feature with the Amex Travel 2X feature to receive a total of 4 points per dollar on airfare.
HOWEVER, American Express practice frequently differs from written policy in the customer's favor. I would make a single purchase through Amex Travel and see how it plays out. Bear in mind the points could post at three different times:
1 base point for spending a dollar
2 bonus points for buying an airline ticket
1 bonus point for booking through Amex Travel
If this is the experience of folks, then it makes sense..