Why do you think they're the same frames? If you look closely, there are a couple things that appear different, including: cable stops in different locations (headtube versus downtube); Defy has a braze on FD, BD's FD is clamp on; Defy appears to have a rack mount. Then there's the welds...maybe it's the white paint on the Defy but they appear much better than the Gravity.

Same geometry <> same frame.