That's not entirely true. I used an application a few months ago (June 22) that did exactly that. That's the app:
apps.facebook.com/xerolasbyvrisko/
They were doing a contest with a trip prize. And the app gave me points for inviting friends based on the number of friends I called via FB invite system.
You can go to my wall to verify it. (
www.facebook.com/manos.mantzas) Look for (Ask to be my friend if you can not see it.):
Μόλις έστειλα προσκλήσεις στους φίλους μου για να αναμετρηθούν με τον XEROLA by vrisko.gr και ανέβασα την βαθμολογία μου!
Φύγαμε για Ανδαλουσία; O XEROLAS by vrisko.gr σε στέλνει ένα μαγευτικό 4ημερο!
apps.facebook.com
Παίξε καθημερινά, προσκάλεσε τους φίλους σου, μάζεψε πόντους για να ανέβεις επίπεδο και να έχεις περισσότερες πιθανότητες να κερδίσεις!
Like · · June 22 at 6:17am via Xerolas by vrisko.gr
Sorry for the Greek, it's a Greek app. You can use Google translation to understand what it says.
If they did it, there must be a way.
Also,
apps.facebook.com/causes/ gives you pledges to invite a certain number of friends to a specific cause and keeps a track on how many friends you invite, again via the FB invite system. How do they do that?
Thanks and kind regards,
Manos