I think its a particularly American affliction: to know ones roommates in advance. Perhaps its an artifact from the formative years, where the shock of living with a stranger is learned for the first time, and subsequent entrance into society is predicated with a desire to not have "a roommate experience which sucked".

In Europe, the roommate experience just sucks - from the get-go - because nobody wants a roommate, really. Americans, unwilling to fess up to this fact, seem to have created machinations designed to facilitate this ease.