Pierre Curie was killed in a street accident in Paris on April 19, 1906. Marie Curie died in 1934 of leukemia, thought to have been brought on by her extensive exposure to the high levels of radiation involved in her studies.
Not to take away anything from their achievements, but many people since have died of leukemia who it does not appear were particularly exposed to radioactive materials.
Isn't it possible that they both took full safety measures?