Jam: Yes, I think most JWs that wanted to get out of jury duty said they had a personal religious objection. The medical reasons and old age that you mentioned are probably the only things that will excuse a person from showing up entirely, but that doesn't mean that people can't be excused for some other reason once they show up. I suspect that most judges would let you be excused if there is a religious objection. They might question some prospective jurors a bit further if they aren't convinced that it's sincere.
I believe there was an article in one of the publications about 10 years ago that basically said it's a conscience matter, but not to tell the judge that JWs are not allowed to serve on juries, since it's a personal decision.
As to education, there is no educational requirement to be on a jury in the U.S. Complex cases are often decided by jurors with a limited education. Just the way our system is.