Yeah, it's not like you'd use this to figure out who should be paid the most, - it's "who should I hand the phone to" when someone calls several years after a project finishes, and if that's wrong occasionally it's ok. And, there's no incentive to be #1 in the result :)

The reason it works is that people write commit message like "Fix X for ACME Corp", and the project leads tend to work on the project for the most calendar time - they may not have the most commits if they have to attend meetings, but after a project/release "finishes", one person ends up sticking around for a while to handle any issues that come up. That naturally gives them some small commits.

To me the risk to me is that this may not generalize, since different projects/products are run in varying ways.