While I don't disagree with you, the problem the author is saying is that end users don't realize that, and contact the author directly even when they are using an out-of-date package from a distribution, and the author doesn't have an immediate way to determine whether the problem is with their code at the version they released, or an older packaged version.

While it's technically true that a free software author owes nothing to any of their users, it's a legitimate problem that there's no good way to selectively offer help and support to those getting the software directly but not to those getting it from a package.