It isn't a case of needing a day for Christmas shopping as much as it has just become a tradition for the Christmas sales to start the day after Thanksgiving. Most people have that day off and so they are available to shop. So, over the years the sales have become more and more extreme (last time I was home on Black Friday I went clothing shopping where the clothing was 80 percent off on that day) so that they can compete to get those shoppers through their door on that day. You wait to see what loss leaders the big chains are going to have (often not made public until that morning or the day before)..when I was home for it two years ago Walmart was doing Laptops for $200. Of course, each store only has a limited number of the big deal products so it becomes a case of getting there early and people going nuts to get them.
I just go get cheap clothing
Personally, Thanksgiving is the one holiday I miss the most when I am not in the States. It is the one day that more or less everybody celebrates as it isn't based on a particular religion and it is really about family. Sort of the yearly gathering of the clans.
Though, I will admit that having one day dedicated to overeating and watching sports and the next day dedicated to capitalism is just about the perfect American holiday
