In the hope that Ford Engineering may monitor this forum:
In reading the 2013 Escape Owners Manual ( at motor service.com ), there was a Note in two places prohibiting attachment of a bike rack to the lift gate. No such restrictions are posted in the manual for my 2008 Mariner. I have a Thule 911XT rack, which is in the list of racks tha Thule says fits the Mariner. Thule also specifys this same rack as fitting The 2013 Escape.
Just some background, but on the Mariner, with two bikes aboard, I always grab the rack and move the two rack bars up/down and left/right to check for security/looseness prior to driving. I have never noticed sheet metal motion at the six attachment points ( since the six straps to the attachment are canvas, and since the rack bars are cantilevered structures, there IS flexibility built into the rack design ). Point being that, if anything, the doors on the 2013 design appear heavier/stronger than the 2008 Mariner doors, so the reason for the rack limitation isn't obvious.
I sent an email to the dealer requesting confirmation of the Owners Manual instructions.