Pizza was originally made as a food for the poor. It still is a great value, even if it's more upper class.
How much do you spend on food everyday? If you eat out cheaply, you pretty much have to spend about $5 per meal; think macdonalds, a sandwich, halal food. Pizza seems the same way, no? In fact, Pizza can be cheaper than groceries!
Think about it. If you're a bachelor, if you order a pizza, it's worth four meals (2 slices a meal). Josephine's large pie is 9.99. That's 2.50 a meal. If you buy your own bread and coldcuts and swiss cheese, it will come to 2.50 a meal. A single small package of broccoli is 1.99.
A family of four can eat for a night for $10.
This is not to say that pizza is cheapier than buying in bulk all the time. But if you're going to skip cooking, and doing dishes, and ending infighting in the family, you can certainly do worse than pizza. As I wrote about earlier, Pizza is a wholesome food, so there's no guilt in that department.