I would not worry too much about the stats for the USMLE. They fluctuate every year. For example, a few years ago everybody from Pittsburgh passed (that is a 100% pass rate), so it would have tied for the highest pass rate in the country.
Most schools have a pass rate near 98% (there are usually one to five people who fail depending on the class size). Reasons for failing will vary, some people may be sick when they take the test, others may have had a death in the family, etc. If you go to an American medical school, then you will pass the USMLE.
If you are accepted to medical school, then it is much more important to select a school based on the city, the parking, the school's teaching methods, the school's support system, the happiness of the students at the school, the financial aid packages that the school offers, etc.