These are very small gender differences. I think there's both biologically based reasons and culturally based reasons that lead parents to talk more to girls than boys. They talk more overall, so they talk more about past events. Stereotypes about gender and emotionality also lead parents to talk to girls about emotion. But, frankly, I think there is something coming from the girls themselves.
Children are active participants in their socialization.
If they don't want to sit still and listen, they won't. Susan Nolan in California proposed that theory, and there's some evidence for it. Anything done to extremes can be unhealthy. People definitely need to talk about their emotions, but if you do nothing but reflect and talk, then you can just stew in it, and that's not good. There needs to be a happy medium.