According to a statement from US News.com editor Bob Morse:

Tuesday afternoon, after the rankings had been released, the Oracle of Delphi got in touch to inform us that per capita expenditures had been given too much weight in the formula, and had to be reduced by 5.731 percentage points, which were to be redistributed among employment rate at graduation (+1.21%), faculty/student ratio (.49%), volumes in the library (.21%), bar passage (.89%), and reputation among lawyers/judges (2.269%).   We did raise with the Oracle the fact that only 17 lawyers and judges in the country respond  to the latter survey anymore, so she informed us that percentage should instead be applied to a new category, "proportion of the curriculum that involves the study of law."

These revisions changed the rank of every law school, excerpt Mercer (which remained at #127).  Yale even dropped from #1 to #14.  The full revised rankings are here.