It is actually a violation of ICANN policy NOT to update whois info.

"...false Whois information can be grounds for cancellation of their domain name registration. Registrants must review their Whois data, and make any corrections."

There is plenty more legalistic mumbo-jumbo if you want to read it but bottom line is, if whois is inaccurate, you are in violation and the registration can be revoked.

http://www.icann.org/en/resources/registrars/whois-policies-provisions