Thanks Scott, i like it when i'm spot-on!
Greg- people have been referring to the Pop reports since the late 90's. The savvy collector likes to know how many of each card exists, so a personal value can be placed on it. it's all subjective obviously, but knowing the pops helps tremendously. a 1 of 2 none higher is a very tough card. 1 of 8, 5 higher, not so much. this rings true across the board, whether it's a Plank, or a McGraw Polar Bear. supply/demand.
It can never be mentioned too many times, that the PSA pop reports can be very misleading, as there are TONS (61,944 to be exact) of cards that fall under "unknown" backs, because PSA only starting listing the pops by backs about 4 or 5 years ago. so if a card is 1 of 2 none higher under the "Polar Bear" section, that's not to say that 15 more don't exist under "unkown".