Beneath the law, beyond the validator

O say, can you see? If not, can you sue?
Designing With Web Standards made the point that an inaccessible site could get its owner in trouble. Now a blind student is suing Target, claiming that its inaccessible site violates the Americans With Disabilities Act and various U.S. state laws:
Unitless and Somewhat Slightly Dazed
Although the W3C validator claims that A List Apart’s CSS is flawed, our CSS is actually fine; the validator has a known bug that causes it to incorrectly flag unitless line-heights as errors. So why write unitless line-heights? Eric Meyer, who created A List Apart’s CSS, explains. His post is not only the best primer I’ve ever seen on the subject, it is the only primer I’ve ever seen on the subject—and the only one you need.