I'm not sure that's even true. RFC 6761 says "IANA currently maintains a web server providing a web page explaining the purpose of example domains."
Saying "currently" implies it's not guaranteed to always be true. (Although it's more likely to stick around than a random domain registered by a hobbyist.)
Saying "currently" implies it's not guaranteed to always be true. (Although it's more likely to stick around than a random domain registered by a hobbyist.)