Perjury is not enforced anywhere but the most egregious cases. Courts are filled with lies told by professional liars and presided over by liars that made a career out of lying. They never eat their own, because it would shine too much light on their own practices.
Perjury based on _belief_ that they own the copyright, as I understand the DMCA. So being an idiot who doesn't understand copyright (or based on an erroneous automated process) is considered a defence.