Retina MacBook Pros are rather delicate, specially the upper case holding the display. I think Bob's assessment is close if not spot-on. I would pack accordingly. When I travel my older, less-delicate MBP goes with me in my backpack. If it's car travel, the backpack is set away from any heavy or rigid cargo so it doesn't get damaged.
We are not Apple employees with access to unpublished specifications, but instead end users like you. However, I've been here a LONG time hand have never seen a weight-bearing specification for any Apple product since the flat-case PowerMac G3s that were discontinued in early 1999:
