I couldn't help but notice that the Arduino Yun doesn't have a 5V voltage regulator. The Arduino team should add it to the board so the board is not so easy to fry.
Well, why does the Arduino Yun not have a 5V voltage regulator?
It's a 3.3V device - having a 5v regulator would make it too easy to connect to 5V devices and damage the IO pins.
Thank you, CrossRoads.