If C was the only language, then a vast body of experience would exist in it and no-one would be writing new code with off-by-one errors in it. What we have right now is everyone "knows" many languages, but actually has little experience with each one. And given the chance to use a new language, we jump at it, even tho' we all know better.
Given the vast body of experience we do have with using C and given that we are in fact still writing new code with off-by-one errors in it, I'm not sure this argument holds much water. There are plenty of developers who have decades of professional experience programming in C, and some of those people are really smart and make software that millions of people depend on, and they still make those mistakes. A bad workman might always blame his tools, but even a good workman will do a better job with better tools.