Law school is the choke-point for controlling entry into the legal profession, and the process of accrediting law schools is effectively controlled by the law professors (AALS) and the practicing lawyers (ABA). Historically, the law schools have not provided the market with accurate, useful information. That created a vacuum that the US News & World Report filled with its ranking system -- which, depending on your view, may be inaccurate and not useful, but which certainly is a best-seller.
Several forces are conspiring to increase the flow of information: the rising cost of obtaining a law degree; the efforts of certain professors to develop competing ranking systems; and the compilation and release of data sets that facilitate statistical studies about life "After the JD," about the effects of affirmative action on generating lawyers, about the effect of law school debt on public interest lawyering, about increasing uniformity in the educational background of newly hired law professors, and about the elimination of innovation in legal education. The blogosphere and law student discussion boards have accelerated the dissemination of all that information.
Will all the new information encourage innovation in legal education? We can hope. My wish list for the future would include increasing transparency into law school costs and the return on investment of a law degree; increasing diversity in law school structure and approach; increasing sources of rankings so that USN&WR is not the only game in town; and decreasing costs of obtaining a JD. Two trends that bother me: the use of citation counts and download counts as a proxy for the quality of education, and the dominance of just a few schools (Harvard, Yale, Columbia & Chicago) as sources of new law professor hires.
(These issues have recently been discussed on too many blogs to count, but general hat tips are due to Conglomerate, Goldman's Observations , Volokh, Balkinzation, Leiter Reports, Legal Theory Blog, and TaxProf Blog, among many others.)