In college, I was a library assistant for ten hours a week at $7 per hour. This was my spending money, and I stretched my dollars pretty far. These days, my wife and I work full-time, there's more than $70 a week for the household, and the spending breakdown is different. There's a mortgage to pay and a kid to support. There's a retirement to plan for.
Spending changes a lot depending on your situation. (Yeah.) It's a good indicator for what people care about and what they need. It's also a good indicator of where the economy is at.