Display Name – Stored in 2 places?

I am wanting to work with the wordpress Display name, however I have realized that this seems to be stored in 2 places in the DB:

wp_users > display_name
wp_usermeta > meta_key (with the value of display_name)

If I do:

get_currentuserinfo();
echo $current_user->display_name;

or

get_bloginfo( 'name', 'display' )

These seem to be pulling from the wp_usermeta.

Questions:
1) Why 2 fields?
2) Where is the wp_users used at?
3) Is there a function to reference the one stored in wp_users?
4) If I am updating the display name, should I be updating BOTH of these fields?