Note that in a lot of localities, people customarily buy food every day. So if they buy eggs, it’s because they intend to use them either today or tomorrow. So they don’t care about shelf-life as much as people who stock up once a week or every other week.
These people recommend using a fridge for optimum freshness as a constant temperature below 20C is best. It appears that it’s the constant temperature/lack of temperature fluctuation that is most important. Supermarkets don’t use a fridge as they are below 20C and it reduces the likeihood of significant fluctuations (eg from fridge to hot car).
It seems the best before is 28 days after it was laid but that an egg can last 10 weeks if stored cold.
According to the American Egg Board,
Assuring Food Safety
Shell eggs must be transported and stored at a temperature of 45°F or below at all times. Proper storage and handling are important in maintaining quality. If not refrigerated properly, Grade AA eggs can rapidly degrade to Grade B eggs. Eggs kept at room temperature (or above 68°F) may lose more quality in one day than in one week under refrigeration.
Kept under proper refrigeration at 45°F or below (do not freeze), eggs will retain their quality for several weeks. Cool temperatures slow or stop the growth of most bacteria. Eggs should be stored in their original packaging materials to prevent the loss of moisture. Store eggs away from foods such as fish, onions, apples, and cabbage as eggs can absorb strong odors.
Here is a cool site featured a few days ago on AOL, IIRC. It gives you the lowdown on what to do to keep food safe and when to chuck it.