I don't know how recently you've been a college student, but Facebook still offers a large ammount of value to that demographic. I would hate to make 100+ phone calls to invite people to a party, or to spend the money/time making and posting flyers.
Sure I'd jump ship if another platform provided more value, but that's (somewhat) different then a fad.
i haven't been in college for 10 years now and i still use facebook (and twitter, and livejournal) to broadcast party invites. there are about 5 people whom i like, and see in person regularly who do not get their news that way, and they get an email about those events.
funny enough, i never set facebook status updates or read anyone else's. i guess creating an event posts it in your stream, but the direct-invite and invited-by-friends feature is the extent of my use of facebook (people do message me on there and i reply via email).
my parties generally have a good mix of highschoolers to 60 somethings. i'll grant you that 2/3 of the sixty somethings are my neighbors and they get the email invite, but a lot of the 50-plus social crowd in portland, OR is on facebook.
the other benefit to using a tool like facebook to do (open) party invites is that people can invite their friends. most of my parties are open; i trust my friends' judgment not to bring/invite assholes. and it works out remarkably well. i've hosted thousands of people at around a hundred parties (some are smaller dinner parties, but still open invite) since i started this strategy, at least half of whom i did not know at all, and only 2 things have ever been broken/stolen. total value lost: $80. total connectedness gained & fun had? incalculable (but huge).
WORKSFORME, without being my only or even main method of socialization (which is decidedly in real life).
Sure I'd jump ship if another platform provided more value, but that's (somewhat) different then a fad.