These studies don’t do anything but prop up existing views. One DNA sequence that was found common among sampled folks with PreColumbian American ancestry was found in just one sampled person in Asia. The conclusion drawn? That that one person in Asia carried a DNA sequence that had otherwise died out in Asia, but had been carried into the Americas by someone in the small, Beringia-walker population; obviously, A) this should show that reliance on DNA doesn’t make sense, because the arguments are constructed to justify the results (the DNA sequence isn’t found there in great numbers now, therefore it must always have been uncommon, or died out for mysterious reasons, or just hasn’t been found because so few folks have been sampled worldwide), and B) that the Bering migration route didn’t have a one-way sign, or a limited time frame.
Latest stuff:
http://news.nationalgeographic.com/news/2001/07/0731_wireearlyamericans.html