I've actually always been suspicious of this. I've never run my domain name through a WHOIS service, but simply entered it in my browser's address bar (though I guess it's possible this isn't "safe" either) to see if it was owned or not.
Fools ignore complexity. Pragmatists suffer it. Some can avoid it. Geniuses remove it. -- Perlis's Programming Proverb #58, SIGPLAN Notices, Sept. 1982