Interesting topic Mat....but I'm going slightly off it, so bear with me!!
I'm not sure what the reason is....I'm assuming it's to do with the quantities produced....but whenever you buy a basketball boxes or packs from the US you always seem to pay fairly good $$$ for it, whereas the equivalent baseball (or even NFL) item can be picked up a lot cheaper. In my experience there is always more competion when bidding for NBA items on Ebay than other sports
Baseball and NFL are bigger markets in the US than the NBA, yet here NBA has the biggest following. Why is it so???