Hear me out. Did you see the great be honkin' vent on the top-right side of the XBone (when horizontal)?
Very, very, VERY few devices have a major vent on top. I've been planning to build a gaming HTPC the size of the ps4, and I have not found one case that makes sacrifices to size or cooling capability in order to avoid having a large vent on top.
And I think I now why: Obstruction.
My cousin usually leaves a game or to piled on top of his PS2 (stuff falls off of the PS3), and I realized that many people (including me) when watching a show will put the case for a DVD on top of the DVD player.
Now here's my guess: There may exist a scenario where people place game cases or other obstructions on top of the XBone, which obstructs airflow enough to prevent proper cooling. I can't say how likely this is, only that I think it may be possible. It won't be a common as the RROD which just needed a little dust and a warm room, but I think this might affect a small number of people.
Thoughts?