Digital BW, The Print

I am puzzled by the following.  If people are reporting very attractive results using BO 
at 2880dpi on the 2100/2200, why is it that when using QTR it is recommended to 
use 1440x720HQ because 2880ppi floods the paper with too much ink?  Presumably 
in a deep black area BO @ 2880ppi would approach maximum ink deposit, exceeding 
1440x720HQ by a considerable margin.  

Steve