> realistic way to get out of, e.g., by utterly bombing on an exam
> or missing a few assignments early in the semester.
You've pretty much hit the nail on the head. The authors of _Grading For Equity_ spoke at my school and the reasoning they gave for eliminating 0-grading (i.e., not using 0 as the lowest possible grade) was because it's basically impossible to recover from. Ideally, a student who masters the material by the end of class should get the same grade as one who masters it at the beginning; being fast or slow shouldn't factor into your grade, but with 0-grading, like you say, an early test or assignment can tank your final grade, even if your knowledge eventually catches up to what it should be.