Uuhm, to clarify, at least this is how it worked for the people who were on course with me two years ago, and explained to us by the clerks:
It had nothing to do with whether or not you were married, it had to do with your residential situation.
The military finds it silly that if you are posted away from your primary residence, which you are continuing to provide for while away, that you should be required to pay further.
Just like on civvy street when your job sends you off for a few months somewhere for training or otherwise, your room & board is paid, the same works for the military. If you are permanently moved, the military, like the civilian world (good companies anyway) helps you move, but usually you pay for your permanent residence afterwards.
So, if you are married, chances are your wife is living somewhere, and that is your permanent residence. If you are on course, the military can not reasonably expect you to pay both for your share of support for your residence and where you are staying on course, you dont pay.
If you are single, this works as well for the following examples: ROTP Civy U students could elaborate, but the ones on my course who were renting appartments (ie not living with mommy and daddy during the school year) still were paying for their rent and utilities, etc, back home. Since they would be returning there at least for 3 more summers until school was done, it was a permanent residence, and they didnt pay for room..... and since R&Q are interlinked, you dont pay rations either.
For most singles, you are stuck paying, because you are entering the forces and should be terminating your lease, since you will invariably be moving as soon as training is complete, and have no need for your residence back wherever you had it as a civvy.
I think I made this sound more complicated.