The way the "jury of your peers" is selected in the american justice system means that sometimes if a person actually has any knowledge in the field the case is about (say a computer scientist in a software patent infringement case) they will be filtered out in the jury selection process. On top of that, jury duty is seen as something to be avoided, so there's also the adage that juries only consist of people not smart enough to get out of jury duty.

In contrast to Denmark, where in a lot of cases the jury is the three judges preceding over the case, or in cases where there's a real jury, they jurors have some form of law degree