* Authorship information in a source file is part of a distribution/source attachement. Version control isn't. We don't have an AUTHORS file, which would be the normal, recommended way to palliate this.
* Whatever the license permits and the author's will, the author may not be able to give up moral authorship (this is e.g. the case for French citizens according to French law). Though those considerations are very much superseded there (French law wouldn't apply even if Tim Clendenen was), and we are not obliged to pay heed to authorship in any way, this is the nice way to go about acknowledging that bizarrery.
* On a non-legal level, making authorship information proeminent and easy to find (i.e. recognition) is in general the Good Thing To Do ™. In general, the more authorship information in your project (as long as it is correct and however incomplete), the better.