QTR-Quadtone RIP

I read in the QTR-User-Guide that all formats(RGB or 16-bit grayscale) 
are converted into 8-Bit grayscale.8-bit is only 256 gradations of the 
brightness.

I know that the Sources(Digicams) does not produce nothing at all 
better under normal conditions. But there is 14-bit 
Consumer Cameras on the Market now which can produce 16384 steps of 
luminance. 

My question: Is the bottle neck the printer-systems anyway? or why 
this limitation on 256 steps?
 

Thanks,

Andreas Engi