Could it be that those bikes were demos? As-new, the performance difference between 105 and Dura Ace (not Di2) won't be too significant and the bike shop can save money that way. High-end bikes like those listed usually sell as framesets, so if a customer likes a particular frameset, the shop can then build up the new purchase with something more aligned with the expensive frame.

If you were so curious, why didn't you ask?