I agree with the other commenters that say thats a bit harsh to completely fail them. I was in my third CS class in college and I left out a semi colon on a test and my teacher said, none of the code would work from here, so the answer is just 100% wrong. Even though the rest was 100% correct. I made the argument that if I was sitting at a computer, that would have been less than a 5 second mistake, or something I would have noticed in the syntax highlight, but he insisted it was a complete fail. I never understood that, but I think it relates back to the days when the professor learned on punch cards and one small error was more costly than today.
Another thing is, when I was learning to program, commenting was something I used to keep things light. Sometimes inside jokes or random bits of code that were terrible that would make me laugh once I had the final solution. In my opinion, unless the assignment was designed to teach proper comments, why not let students be creative with their comments, even if its redundant to you.