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I'm not sure that that makes sense. Have those people never read a newspaper, or a book, or done an assignment in class?

Specifications and annotations on construction drawings are typically all caps, as well. In that context, it looks more official and also more legible at various magnification levels.

And U.S. National Weather Service communications are also entirely in upper case. I guess that there are still remote locations that receive them on teletypes that only have upper case. Here's an example:

http://forecast.weather.gov/product.php?site=NWS&issuedby=OK...

I think it is a thing of people who read a lot of text.