I think this is mainly because Black Friday sales aren't usually confined to Friday any longer, but generally last nearly a week and are usually more aggressive than any sales in December. Plus, Black Friday is becoming much easier to shop (at the expense of the poor retail workers just wanting to spend Thanksgiving with their families). In the past, the best deals were usually confined to a six-hour or so doorbuster window, and the stores would be so flooded that going involved waiting in line for hours just to find out everything was sold out. Now, with stock boosted and the windows expanded to that Thursday and Friday, and considering most stores stay open all night, it's easy to walk into a thinned out store, pick up everything you want for the holidays, and to be out within a much shorter period of time.
