Fifteen years ago, Bill Hicks performed a routine on Letterman that never aired. The content wasn't appropriate -- maybe he didn't do the material he said he was going to do -- maybe some censorial types objected. A few months later, Hicks passed away from pancreatic cancer -- a condition he'd hidden from all but his closest family members. Last night on Letterman, Dave apologized to Bill's mother and aired the never-aired segment.