I'm really interested in a GitHub person's take on this (holman?). Is my notion of the balance reasonable? (You've got the data, I'm just guessing with it.) Do you think you're likely to assess improving GitHub's 404 page at least?
You bring up some good points, and we're always improving pages like these (the 404 itself has gone through a few versions this year already).
I don't think the answer is forcing the canonical URL on every page request, though. I think it's important to retain branch names instead of the full sha. I find this, for example:
It'd be great to be able to support file renames and deleted branches better in the product, but that takes some time to build out. Hopefully we can do better with that in the future (and we have been working on things like this recently- supporting repository redirects was a huge one, really).
