This would also be a huge issue for rebase workflows, because rebasing changes the commit SHA. Every commit I rebased would end up belonging to me, not the original author.
It's worth keeping in mind that what GitHub does now is what _every_ other git client does, and it's in GitHub's best interest not to confuse users (or to make it look like they're privileging a GitHub-based workflow over a standard git workflow).
> You may be wondering what the difference is between author and committer. The author is the person who originally wrote the patch, whereas the committer is the person who last applied the patch. So, if you send in a patch to a project and one of the core members applies the patch, both of you get credit — you as the author and the core member as the committer.
Try it by setting the author on a commit you make. Github displays it just fine. I used to use it in school when working with non-comp-sci students on collaborative work (for instance, a report written in LaTeX).
[0] http://git-scm.com/book/en/Git-Basics-Viewing-the-Commit-His...