While I agree that the UI is a bit subtle in the difference, Apple isn't trying to screw anyone. If you're really trying to save battery life, Airplane mode is the way to go. It totally turns off the wifi and the LTE radio (which is very battery draining).

I like this change because when I turn just wifi off it was always because of an acting up network. Now that I don't have to remember to turn it back on is a good thing. My guess is that Apple has a lot of data, and found that this behavior is what most people want.