I'm going to preface this response by saying that it is in no way, shape, or form meant to come across as snarky or negative.
Maybe it's issue of interpretation. I take "extra" literally, i.e. beyond what is usual, expected, or necessary. In the past I've seen "extra mile" exercises to mean, "good skill/information to know but not necessary for the exam." So, if I'm weighing my time (class, work, family, a wife who has only seen the back of my head for the last 5 weeks), I might be tempted to skip the extra mile in favor of brushing up on ruby or catching up on some household chores, etc, etc. And if the extra miles are mean to impart research, problem solving, and organization skills, critical to passing the exam, then why not simply move the extra mile exercises into the main body of the course?
If you're not even putting the time into doing the majority of the Extra Mile exercises and lab systems, you're not obtaining the skills to do well on the exam (or out in the real-world).
I don't have a problem with extra practice, and I think it's been made very clear that we're supposed to hone our skills on the lab machines. My issue is with extra mile exercises that cover concepts that may or may not be on the exam but weren't covered in the lecture.