1. The assumption that all students start at 100 and points are "taken off." This is the reverse of how grading actually works. Students start with 0. If they meet the minimum requirements, including basic expectations for editing, proper format, and minimum source requirements, that skyrockets the grade to 70% or higher. The rest of the potential points have to be earned. How do you "earn" those? By going beyond the minimum expectations. By showing you are not just hoop-jumping. Paying attention to editing is a good idea, as is setting up topic sentences and other elements of the assignment that your instructor has been harping on for the last four weeks.
2. The assumption that the student is a customer who is always right. This isn't WalMart. Heck, these days even WalMart requires you have a receipt to return something and get your money back. In the classroom, if you want to dispute a grade, you better come prepared to demonstrate you did, indeed, earn it. In the situation where this demand was made, the paper was riddled with errors and it had 2/5 of the required research. That's like trying to return a old console TV at WalMart with no receipt. Sure, it's a TV and maybe it was purchased at Walmart (but who knows); it doesn't, however, meet the standards to receive a refund.
3. The assumptions that writing skills don't matter as much as "hard work." Effort is not grade-able. If it was, we'd all be turning in spreadsheets of how much time we spent on each part of the project and the computer could somehow qualitatively assess how "hard" we worked. We could just get rid of my job and have a computer use collected keystrokes and browser history and time logs to determine grades. That's not how it works.