But wouldn't this be teaching developers? They upload the file and Github explains to them that it should be kept secret, and the developer has the opportunity to revoke the file. That sounds like the ultimate way of 'spreading the word', and if Github does disappear, they will have made people more aware. Not to mention it won't affect people who have been doing this all along.
Out of the 3000 repositories which I estimate to be affected by this issue (using Google and eliminating some common techniques used to circumvent the problem), I estimate 1600 of them are not on Github. Even if Github does its best to remove the issue completely, I don't believe it will have a huge impact.
I believe that a better idea is to fix this in Rails. Why is a secret key loaded from the configuration directory? I agree with ajross's comment (http://news.ycombinator.com/item?id=4970347).
This isn't to say that Github should do nothing to control the problem, but more must be done than just that.
Well yes, it could be teaching developers. But you would be teaching a single solution for a single problem. I think it would be better to entice solutions that target the bigger issue on security awareness. All this new tools that make it so much easier to develop complex applications have huge benefits, but I believe they are also pushing new developers away from understanding the concepts behind what they are doing. As someone who started as a designer and grew on my own into development, I've seen this issue first hand.