Yea. They will actually deduct marks. I think your reasoning/logic needs a bit of an overhaul man
Just because the class average is low, it doesn't mean they're going to stop deducting marks... If they said they were going to mark you on something at the beginning of the term, they don't care if the class is failing: They marks the same. Granted, the course is often bell'd, but don't expect them not to deduct grades where they said they would, because there are people who DID go to every lecture/tutorial/lab because of that stipulation, and they deserve some reward over those who didn't, if they were told they'd get one.