Why all blink tutorials use 330 ohm resistor
150 Ohms may be "enough", but it's often still far too bright, so many tutorials keep a lower limit of around 10mA to help the LED live longer without affecting the application. 

You'll probably find that red LEDs are still visible at 1mA and a 330 Ohm resistor with a 5V supply will give about 8.5mA (assuming a 2.2V drop), which is plenty. 

It's really a "lazy" choice that will work well in "most" situations.