That is the standard set by the USDA. You can view it on their website. If you choose to get your Candling /grading license this is the protocol you have to follow.
The USDA set the standard at 45 days from laying for refrigerated eggs. It is recommended that you refrigerate @ 45°as soon as possible after wash dirty eggs and drying. Only leave out eggs for hatching. shelf life for eggs left out is very short.
I am a USDA certified Candler and grader. Here is what you need to know. Eggs have a 45 day shelf life from day of hatch. To test the age of an egg put in a pan of water. If the egg sits on the bottom it is fresh the more it floats the older the egg.