The potential to make alot of money on poplular domains is enormous. This is what happens:
1) you have an incorrect phone number in your domain whois. Perhaps you typed in 555-555-555 instead of 555-555-5555. An honest mistake. Perhaps you moved and forgot to change the phone number part.
All the other info is correct including mailing and email address
2) Someone contacts the registrar and says "Hey, the phone number is wrong on this guys whois.
3) The registrar emails you. They do not attempt to contact you in any other way.
Everyone here knows how iffy email is - emails do not always get through. Also, because your email address is listed in the whois, this email address is bombarded with thousands of spam emails every day, many of which get through your filters. This makes it easy to miss the registrars email
4) After 5-days without your having responded (perhaps you were on vacation) the registrar pulls your domain and the site goes down.
5) Now you are at the mercy of the registrar, who holds your domain hostage for a fee or, worse, sells it to the highest bidder.
I bet the registrar can obtain some valuable domains using this trick.