Les domaines "example" en .com .net et .org sont réservés par l'IANA.

yannick@yop:~$ whois example.com

Whois Server Version 1.3

Domain names in the .com and .net domains can now be registered
with many different competing registrars. Go to http://www.internic.net
for detailed information.
-snip-
Domain Name: EXAMPLE.COM
Registrar: RESERVED-INTERNET ASSIGNED NUMBERS AUTHORITY
Whois Server: whois.iana.org
Referral URL: http://res-dom.iana.org
Name Server: A.IANA-SERVERS.NET
Name Server: B.IANA-SERVERS.NET
Status: REGISTRAR-LOCK
Updated Date: 26-mar-2004
Creation Date: 14-aug-1995
Expiration Date: 13-aug-2011
-snip-
Registrant:
Name: Internet Assigned Numbers Authority (IANA)
Organization: Internet Assigned Numbers Authority (IANA)
Address1: 4676 Admiralty Way, Suite 330
Address2:
Address3:
City: Marina del Rey
State/Province: CA
Country: US
Postal Code: 92092
Phone: 310-823-9358
Fax: 310-823-8649
Email: res-dom@iana.org
Registration Date: 11/01/2001
Last Updated Date: 11/01/2001
-snip-


Ceci est décris dans la RFC 2606

[...] To safely satisfy these needs, four domain names are reserved as listed and described below.

.test
.example
.invalid
.localhost

".example" is recommended for use in documentation or as examples.

Les sites web en question renvoient justement vers la RFC.