I'm currently tutoring my daughter in statistics for the same reason. She's in college and while she's flipping through her homework appliication and her e-textbook, I'm flipping through my old statistics books, plus a couple of study guides I picked up.
Also, sometimes the homework application is simply wrong. (Doesn't every tool/program have at least one bug?) My sister, a teacher, uses one - mandated by the community college where she teaches. Occasionally, she has to override the application so that she can mark correct problems that the application marked wrong. The students alert her, she checks and then overrides when the application is clearly wrong.