If I put my number or email on my page, and I adjust the privacy settings to "only friends", I understand I am making that information available to my friends. They are free to copy that information by hand, or by copy-pasting, into their own address book. I have explicitly made it available to them. Facebook includes information about your friends, such as their birthdays, in your data export. Their decision to not include off-Facebook contact information is a business decision designed to make leaving Facebook harder. It has nothing to do with privacy.