This video of unknown provenance shows a tortoise who has flipped over on his back. He's helpless until another tortoise rescues him by pushing him over.
This incident shows that tortoise do have a feeling of brotherhood in them. We must learn something from them.. http://ezinearticles.com/?Nitric-Oxide-Supplements---Build-More-Muscle-Faster-With-N02&id=4432221
Mmmmh, indeed, it would be quite efficient, evolutionary speaking. Embedding this kind of behaviour is very beneficial for the whole species, and thus, each individual creature. I guess it's instinct, I doubt that tortoises are evolved enough to learn this kind of action.
My guess is that it's not necessarily friendly. It looks like once the helper tortoise is done, he takes a little nip or two at the other's scutes and follows closely (pretty classic breeding behavior). Tortoises are capable of learning but I doubt if that was intentionally helpful.
http://ezinearticles.com/?Nitric-Oxide-Supplements---Build-More-Muscle-Faster-With-N02&id=4432221
http://www.youtube.com/watch?v=6R3BYCT5oWw
(Keeper of more than 40 tortoises)