A27 Addendum
Yeah Paizo did a lot of minor changes, it can be sometimes annoying if you have had 3.5 experience.

Besides that the reason why they changed Regeneration is because they changed nonlethal damage. They fixed the fact nonlethal damage cannot kill you (which lead to silly things like not eating doesn't lead to dead in 3.5) by making any nonlethal past your total hit points into lethal damage. Thus a creature with 3.5 regeneration, but pathfinder nonlethal rules would still die from his non-lethal injuries, which is not the intend of regeneration, hence they changed regeneration. (The more you know, and knowing is half the battle.)

Also, just something to note, but being immune to nonlethal damage and fatigue/exhaustion also means you don't have to eat, drink or sleep, worry about weather and you can run all day at top speed without getting tired. Just a silly it of extra info while I am add it.