after all of the recent BAMS discussion about red/not red cap coloration, altho your mention of the red being redder than usual is duly noted.

your statement about exposed vs buried caps makes me think that exposed caps are the red ones; they just start out pale (B. edulis does too, and stays pale if it remains buried).
Perhaps the reason that an inordinate amount of pale capped ones are found commercially is due to folks harvesting young buttons specifically? In other words, deliberate slection for the more pale, immature forms.

http://tech.groups.yahoo.com/group/BayAreaMushrooms/