I get a ton of spam because of this. However, I'd rather have this system than one in which all the owners are secret. I've had to look up owner information before to contact owners of various properties, and having that hidden would have made that task impossible.
You can hide the ownership information of a house, if you pay extra money, by hiring a lawyer to create an entity and put the entity on the property, but then the lawyer has to put their address, and forward any requests on to you, just like the whois privacy folks.
I think it is a good thing that every domain has valid contact info.