Not necessary, just desirable because people like buying things.
Considering it 'necessary' is actually part of what makes this a problem. If people knew how to want instead of need, they might next learn how to delay gratifying those wants. Instead, desire becomes confused with necessity and suddenly you can't live without an HDTV right now.
The median income per household member in the US was $23,535 in 2004[1]. Unfortunately I can't find a more recent census value for that. In the case of a household with two partners and at least one child, such as we're discussing here, I would think that more than ~$24,000 would be necessary.
