I think the Katniss character was supposed to be deadpan. Her environment is totally depressing and little to smile about.
Lawrence, OTOH, is a "wild child" who says exactly what she is thinking and works at remaining "normal."
True or not, don't know, but I read that her parents wouldn't allow her to try acting until she finished high school...so she finished in 2 years with a 3.9 GPA...got her first acting job at age 14.
Google hunger games Bush administration and you’ll get a million hits.