I haven't done much with android in almost a year + now. Just trying to be helpful
Airplane mode from my understanding will disable all the radios in the device. I think you run into this issue because you have to enable wifi manually afterwards (even when it's already enabled). All the radios would include the voice, data, wifi, bluetooth and any other signals the phone may be putting out. Data will be a separate radio with 4G.
Whereas 4636 will just disable the voice / data radio and not wireless+bluetooth and etc.
From the 4636 screen you can also force your phones band. BE CAREFUL DOING THIS! THIS IS A DIAG SCREEN AND SOME OPTIONS WILL KILL YOUR DEVICE! If you live in a 4G area and have horrible 4G reception. Setting your device to 3G only will improve battery life.
AGAIN BE VERY CAREFUL IN THE 4636 MENU, IT IS A DIAG MENU THAT CAN BREAK YOUR PHONE IF YOU DON'T KNOW WHAT YOUR DOING.
Edit: More for the disclaimer. I know some phones that you change bands on and they will never change back. Please check XDA forums for more information on what you can do with your specific phone.