Respectfully disagree. The quality of a screen can drastically alter the quality of the picture. If they were the same what makes one HD screen differ from another? Some are brighter, more vivid, and have better response times etc.
Ive seen full 1080p HD monitors from cheaper manufacturers that give rubbish quality in comparisoon to a better spec 1080p panel, such as the Apple Display, for example.
LEDs are slightly brighter then LCDs, whereas Plasmas have much better, darker, blacks and brighter whites then LCDs, by far.