This isn't surprising. We all know that Hill's running for Pres in '08 (can't they just hand the job to her? After all, she was born to be President, right?). If she had voted "yes" on Roberts, she stood the chance that he might make ruling on a case before the court that would infuriate Hillary's base (that would be the extreme left). Can't have that.
On the subject of Hillary '08, check out the Dick Morris column in yesterday's New York Post. Interesting.