If you check those links in the OP you will see more than a few stores are opening at 8 pm on Thanksgiving. What they are doing is opening at that time so people can get the non doorbuster but still good sale items. The limited quantity stuff wont be part of the early openings and the ads will say "starting at 4 am" or something similar for the "doorbusters."
I think this is a good thing because it will prevent people who don't want to buy the doorbusters from adding to the large numbers and mob like crowds of those that are going after the limited quantities or crazy doorbuster items. Also it allows people to not have to wait outside overnight.