There's an autonomous level of spending, which includes the necessities of which you speak of, but the higher the prices the less luxuries are consumed, and food levels higher than necessary to remain healthy are luxuries.
You don't eat less bread in a country where bread is the staple food because it becomes more expensive. Instead you pay more for it, thus having less money for other luxuries (luxuries that may even be in abundance).
People don't eat more food as a luxury, they eat other food as luxury. The reason is that people simply cannot (or very rarely) eat more food than what their stomachs are satisfied with.
It is in the common human nature to satisfy your stomach before satisfying your brain.
You could argue that eating more food than neccessary to satisfy you stomach may be a luxury (luxury = pleasure), but since eating more than that makes you sick, it cannot be a luxury because it is not a pleasure to you. If it is not a pleasure it is not a luxury.
You do not get sick of having 10 cars. Therefore there is nothing that naturally stops you from buying 10 cars. So in order to ensure there can be produced enough cars, the prices are so high, that you can only have 1 or 2 cars.
You do get sick of eating more food than what is healthy.
Though you could argue that it takes more food than what is healthy to make you full, but people will naturally eat food until they are full, at the expense of other luxuries.
Overall, the PoliticsForum quiz considers you an individually-orientated, materialist, small-government, free-trade, non-absolutist, controlled-market kind of person, who also seems quite Marxist.