We've had numerous power outages; after being out of power for over a week I bought a heavy-duty generator that can tie into the house wiring. It sucks having no fridge or power. When we had the quake in 1989 in SF, it was a wake-up call to get prepared. No power, no street lights, no gas stations, no cell phone service, closed stores, etc. We knew things would be okay after a couple weeks. But if the SHTF in 2012 it won't be okay for 6 months or more. The zombies will roam.
Most emergencies would put us off line for maybe two weeks as you say. But something serious could knock us down for 6 months or longer. Actually, losing your job in this economy could put you down for at least that long. If the emergency was broader, and the economy was disrupted in some serious way (war with Iran, maybe?) as you say, zombies will roam.
In that case, we'll want a bigger pantry, and a shotgun, and good neighbors we can count on. We'll have to build our own microeconomy in a case like that, and stick together.