[asdfer]

This is the main reason I always hear that people are 'forced' to stay on FB, even if they don't like it: so they can still get invited to parties.

[johns]

That's just (somewhat justified) laziness on the party organizer's part since you can add people to Facebook events that aren't on Facebook by entering their email address. They get a normal invite and chance to RSVP. Facebook membership not required.