In or Out or Both?

Following up on my post, Good Fences and Good Neighbors, I have a quick question for those of you better versed in Web 2.0 etiquette. What does it mean when someone allows you to be LinkedIn with them, but doesn't share their contacts with you. Is this an appropriate and sensible approach to maintaining a reasonable zone of privacy, or is it a basic violation of web 2.0 principles?