I think it's not just the amount of what can be reproduced from a certain work—if it's 10% or 8%—the most important part is how many copies you are making. If you're making a copy for your own personal use, that's accepted in many countries.
However, what I have heard—and I'm not so familiar with the situation in Canada—from Canadian publishers is that some universities are somewhat taking this expression of educational exception in the law to make copies for all their students from one chapter from one book and one chapter of another. Perhaps having one chapter is not too much, but having one chapter from 12 different books and then distributing that to all their students is definitely hurting the business.