Food, Leccy, Clothes are things you choose to buy from whoever you want, rent on the other hand is a fixed cost for the roof over your head that is currently in most cases paid direct to the landlord so it's a case of if you have never had it you won't use it for anything else. Giving it directly to the claimant while cutting other benefits is going to put many claimants in a situation where they have to choose whether to use that money for other essentials. This is not a good idea because ultimately these people will get evicted and be unable to rent non-social housing meaning that they will be put up in travelodges (I have seen this in Tolworth btw) due to the severe lack of social housing. Will this help with the ultimate aim of reducing the welfare bill? Not a chance, if anything it will increase it. Therefore I stand by my original comment that it is the most stupid idea the government has ever thought off.
You make in interesting point about the People Commissariat Of Poor People's Food and I wouldn't put it past this or a future government to do just that using a voucher system like they do for milk. How you stand on such things is determined by how many channel 4/5 documentaries about people with 40 kids or living by sea on benefits you have had the misfortune to watch.