Good code doesn't need many comments. By picking descriptive names for your identifiers, the identifiers themselves become the comments. I agree that the specific example of a comment is stupid and pointless.
I personally suspect that such comments are made by programmers who are insecure of the language and their own abilities, and thus they are rather explaining their own program to themselves as they write it, rather that to the person who will maintain it in the future.
Though of course there are also people who name their variables err, tmp, x, buf, a, b, c etc. If I had named my variable "err" the comment about error location is suddenly necessary. The solution then is of course to give the variable a meaningful name instead.
You will also have to assume that the person reading your code is a programmer. You should never need to teach the programming language to the reader through your comments, unless you are doing something very obscure and unintuitive.