I can't quite follow this. Brighter does in fact mean whiter, since white in ordinary TVs is from adding the RGB primaries (with sometimes a fourth primary), so when each primary gets brighter, so does white.
You lose white detail when color depth is not sufficient (not because of saturated colors).
I do digital photography and you do get loss of detail with over saturation of colour. Think of it as when you have many bright pixles of almost the same colour side by side, the brightness bleeds into one another to the point that you cannot distinguish the subtle differences in the colour. As you make the pixles brighter, then the realism of that colour looses effect. For example if the only way to get a true red is to brighen the pixles, then a red apple would appear to glow rather than just be red. The apple would have less detail and look over saturated to get the correct colour.
I have an iMac. It has a black boarder around the outside.. but if I try and put a black graphic on the screen, the black is not as back as the outside boarder as LED cannot get a true black. Now I can get most whites, but in doing so, it over emphasizes that colour and detracts from the colours around it.
