It's all in the design. The Xbox One runs quieter and cooler. I mean, one EASY way they could have cut down on the heat and not have the fans run so loud would have been to take the power brick OUTSIDE the system. Sony was praised for putting it in the system, but my first thought when they did it was "that's an aweful tiny box to purposefully put more heat inside than is needed". Power supplies heat up. Would rather that heat not HAVE to be right next to the components when the ventilation area is so small.
Beyond that, it seems they sacrificed proper ventilation for sleeker design - which isn't bad in general, but could mean that the PS4 isn't a console that just lasts 20 years. In about 6 or 7, that constant heat from intensive games could cause hardware failures.
Microsoft went as save as possible after having heat issues in the 360. THe console may look like a giant brick, but that brick is ventilated everywhere. Top, sides, back, plus space inside for the air to circulate. My Wii U is literally stacked directly to the left of the console and there is a few centimeters to the right and a few inches behind, yet the console never seems to get too hot or loud. Even if it is on when the Wii U is, it isn't adding extra heat to the Wii U.
Conversely, my PS3 doesn't get too loud, but my gawd does it heat up.Just idling on the home screen, my PS3 can heat up my entire living room during the winter. It's a launch console PS3, so I have a feeling the fans and cooling have worsened over the years. For the brief time I had a PS4 in the house, it felt like I was launching a missle everytime I played games. It was loud and hot - two inconveniences in one.