Also, I like the idea of having health regen just for easy mode.
If you're going to add automatic health regeneration then I still suggest putting it as an option. When the player clicks the easy mode a question would pop up asking:"You've chosen the Easy difficulty level. Do you wish to have automatic health regeneration?"
And that option shouldn't be limited to Easy only. I liked that you could change the difficulty setting while in-game in Human Revolution (I also like how I am using HR as my example all the time). That's a good idea for many games to have including options like health regen.
EDIT: But I am just nit picking. It isn't going to ruin my experience and if I was so stuck up that I wouldn't play a game mode because it had health regen I still found a solution. Play it in full stealth. So all is good with the world. I just feel they could have thought this through.