The Xbox 360 was a uniquely shape console that looked equally as good horizontally as it did vertically. When the console first game out, many gamers chose to stand their console on its end in order to preserve space or just make it look cool.
Unfortunately, with the Xbox 360, standing the device up vertically caused some serious problems. Discs would crack and heating issues could send your Xbox to Red Ring heaven.
With the Xbox One, similar concerns have caused Microsoft to issue a warning for the device: Microsoft strongly recommends not standing up the Xbox One vertically. Unlike the Xbox 360, all the press pictures for the new device have shown it sitting horizontally – which is exactly the way Microsoft wants you to put it.
In an interview with GameSpot, Microsoft’s senior director of product management and planning for Xbox Albert Panello said that Xbox One users could stand up their console “at your own risk” because the slot loading disk drive was not designed to be used that way. Panello emphasized that this wasn’t an overheating problem, but instead was a problem with the slot loading disk drive.
Specifically, the disk drive is not designed to handle vertical loading. That doesn’t mean your Xbox One will explode when you stand it up vertically, but it does mean you should orient it horizontally if you, you know, want it to work properly.

PlayStation 4 and PlayStation 3 users are free to orient their consoles vertically

The PS3 and PS4 both have slot loading drives. Both of these consoles can be used vertically. So why is the Xbox One different? Well, the specific types of disk drives are different. The Xbox One extends a disk tray to users, while the PS4 accepts a disk into the innards of its system (that sounds gross). That may be the reason for the difference between orientation requirements, but Microsoft could simply be hiding an overheating issue.
I guess we’ll have to wait to find out.