(Denny Crane: "Sometimes you can only look for answers from God and failing that... and Fox News".)
The federal courts DID look at it "de novo". They performed a de novo review of the law.
That being said, they did not perform a de novo trial. A new trial would be almost unheard of -- including death penalty cases. The only time I can think of a de novo trial is in the case of an appeal of a small claims court ruling.
The law said "de novo" but never specified which type.