Issue at power on

Using Arduino IDE 1.x
7

The HardwareSerial library (such as used by the Uno) just implements the "wait" as something that immediately returns:

HardwareSerial::operator bool() {
	return true;
}

So it doesn't really wait for anything. They just put that code there so you could add the lines:

   while (!Serial) { }

... and not have to care whether this was compiled for the Uno or the Leonardo.