Then your teacher is admitting that my design only the few tenths of percents surrounding the letter grade cutoffs are worth anything. I suppose it's just a matter of opinion, but I find this system remarkably arbitrary.
I knew that the cutoff for an A was 90%, and I also knew that the grade would be calculated based on my projects and exams. I knew the exact weight of each project and exam too, all within the first few days of class.
I knew what was expected of me in this situation and didn't deliver, so it was my fault for not getting the A - not the grading system's fault. But my 89.4% was so close to an A that I somehow felt entitled to getting one, but as his quote points out, I didn't really deserve it.
I think the point isn't whether or not it's ethical (full disclosure in college would make it so), but whether it's a smart way to do things. I claim it isn't.