Sorry, I should have used "patent lawsuits" instead of "patent trolls". Didn't think I have to draw intestines on stick figures, but there you go. Some people need hand holding to generalize upon an idea, and I guess you're one of these people.
It's as if you didn't even read the summary. The patents are filed with help from pro-bono lawyers working on behalf of Khan Academy. It costs them NOTHING to file patents.