That's my entire point. You need a (number, location) combo to many any reasonable deduction, not just a number.

Sure but that's true about any number, I can't think of any number which adds any value without some context. In statistics, your population is your context and all inference/conclusion depends on the population (local, city, world,etc). For social classes, I'd say the more local the more representative your number, which doesn't mean there isn't a number to represent the middle class.