I think there are probably 2 categories of disaster one can prepare for.
1) Common disaster
The Common disaster is the bad storm, when you get bad storms once every few years. Tornado Alley, Hurricane Alley, these places know this problem. The Northwest gets good windstorms every so often. The mid-atlantic, too. California gets earthquakes. In any event, it's something that happens, has happened many times, and is sure to happen again. It's disruptive, you need adequate supplies to hold you over until things get rebuilt or back to normal, or if you're in the epicenter, give you time to relocate/rebuild.
2) The Uncommon Disaster
Uncommon Disasters are major terrorist events, biohazards like bird flu, massive infrastructure shutdown (pipeline destruction, Interstate collapse, etc), economic implosion that leads to supply disruptions. These are the times where a year's supply may come in handy, and where subsistance gardening, water catchement, and dry storage allow you to live for an extended time without going to the store. If the banks go down for a week or more, and your ATM card doesn't work, do you have enough? If the truck supplying your local food mart doesn't arrive, do you have enough? If there's a quarentine on your neighborhood, and limited supplies are trickling in, do you have enough?
I think #2 is what most people think of on this forum, from what I've seen so far. And it's good to have a stockpile, and a plan. I try to consider the various #1 scenarios as "practice" for a possible #2. If I can keep the family going just fine for a week, cut off from the community for resupply, that's an excellent beginning. By then, in any major disaster, the next move will be clear, whether it's to shelter-in-place, head to one of my distant evacuation places (extended family and friend's places), or adapt to a massively changed environment where the rules are all different (apocolypse scenario).