It is probably because your claim is easily disproven. I have a headless mini in my server room right now that has no problems booting. Turn on screen sharing and you can login and use it just as if you were sitting in front of a similar box with a display and keyboard.
Well, the generation we have doesn't. We just built some DVI connectors with a resistor on the back, to make it behave similar enough to a connected monitor.
Mac minis are fairly different depending on the generation.
