Over 100 top-traffic and government websites from the United States and United Kingdom were examined for evidence of changes on accessibility indicators over the 14-year period from 1999 to 2012, the longest period studied to date. Automated analyses of WCAG 2.0 Level A Success Criteria found high percentages of violations overall. Unlike more circumscribed studies, however, these sites exhibited improvements over the years on a number of accessibility indicators, with government sites being less likely than topsites to have accessibility violations. Examination of the causes of success and failure suggests that improving accessibility may be due, in part, to changes in website technologies and coding practices rather than a focus on accessibility per se. © 2013 ACM.