I've talked to multiple people about this and it's been a source of confusion. It seems that the default setting for familiar cards is a group of cards from the base set, and the default setting for which cards to put in a random kingdom will respect everyone's familiar cards. So that means that if two people play each other, unless they have changed their default settings, they will get the same base-only kingdom every time. People who have had expansions transferred over, myself included, have been confused by this.
Some default setting probably needs to change, or some kind of very visible notification needs to be displayed, otherwise people might think that Dominion is a boring game with only ten kingdom cards every time you play.