The system will not work in many places. It is based on honor code i.e, no body will take an item without scanning it. Most supermarkets have razor thin margins - add theft and they will not be able to make money.
As to "Razor Thin Margins" that relative, Walmart got in to Groceries because they could make more money then when they were just a General Goods Store. While the per item margin might be slightly lower than General Goods the volumes are WAY higher thus making it over all more profitable. That also means loss is actually less impactful