one of the major things causing the discrepancy may be that jury selection processes are very different. from this page it looks like in the UK jury selection is a matter of 12 people out of 15 called being randomly selected by the clerk of the court, whereas from what I have seen in the US, a much larger pool of jurors is called, and then the prosecution and defense exclude people until a jury is decided upon.
That would seem to indicate that for the same amount of court activity a lot more people get called for jury duty in the US.
When I did jury duty in the UK, there were about 150 people called up to our local Crown Court in the same week as me. They had about 8 new cases starting that week, so several times during the day, they called out 16 random names from the pool and the potential jurors all went into the court room. Out of the 16 names, 12 were selected at random by the clerk and the remaining 4 went back into the main pool. By the end of the first day of jury duty, there were about 50 people left in the main pool and they came back the next day (and the next) to see if they were going to be selected for a different trial. If a trial ended within the 2 weeks of allotted jury duty time per person, the jurors just went back into the main pool again with the possibility of being selected for another case.
It seems odd that in the UK the prosecution and defense cannot exclude jurors.
What if you personally know someone involved in the case?
They can exclude them - when the jury are selected, the members of the courtroom (including the defendent) are asked if there is anyone they object to being on the jury and if so, then that person will be asked to leave the jury and another person will be selected.
Also, the members of the jury are asked if they know anyone in the courtroom or any of the names of people involved in the case and if they do, they cannot serve on that jury.
