Omg, I guess I'm the only loser who's always put the opening up towards my head!!!!! I think because I don't like seeing the buttons/opening at the bottom of the bed-- it just looks so noticeable to me (we don't have a foot board). I guess the buttons/opening have never bothered me or my face!
I did get cheap Ikea duvets for DS2's bunk beds though and they just have an opening on the duvet with no flap or buttons so I put those with the opening towards the end of the bed since the opening would be tucked in and covered by the foot boards. Plus, those duvets have a decorative trim up on the top, opposite the opening so I wasn't as confused!
Thanks everyone for solving a lifelong mystery of mine!!!!