And I hear your RE adding another tool, as I'm very cautious about that myself. That said, `git am` is "git cannon", and all hub is really adding is the ability for it to slurp Github urls as well as Maildirs.
Neat, related trick: add ".patch" to the end of any PR url on Github and you'll see a formatted patch for the PR. All hub is really doing is slurping that and passing it to git as though it came from a mailing list.