[mbreese]

The absence of evidence is not evidence of absence.

Another rationale is that they would have needed a unanimous opinion to overturn the patent on prior-art. And since they weren't going to get a unanimous opinion, they skipped it because they couldn't over turn the patent.

Without knowing all of the jury instructions, it hard to know exactly what happened.

[danielweber]

The absence of evidence is not evidence of absence.

I've been agreeing with your other points, but I must disagree with this specific. Absence of evidence is definitely evidence of absence. Keep in mind that "evidence" is not the same as "proof."