A couple of teenagers from church just added me as Facebook friends, which means I’m getting another onslaught of application invitations. They’re sending me Pokémon things, Are You Interested invitations, Flirtable Pet Trees, and whatever else they’ve come up with these days.

Getting the invitations is annoying, for sure, but I think it’s also a reflection of the flawed social model that Facebook has started – and that everyone else seems to be following.

The reason why it’s a good idea to build social applications into an existing social network is because of the user base, obviously. Everyone is already a member, and connected socially. You can use that existing structure to create some great functionality – see what movies your friends are watching, get music recommendations, etc. etc.

But how in the world can you benefit if each member has to add the application individually? Music recommendations are useful if they come from all your friends – but not if it’s just one or two. If each person has to add the application, then the existing social structure means absolutely nothing. There is little to no benefit to having the functionality built into an existing social network, because you don’t actually have 70 million people linked together! You only have the few that have added your app, and then you’ve made it really easy for them to uninstall.

Wouldn’t it be better, for both the user experience and the third party developer, to instead have a few really good pieces of functionality that get built right into the site?

And I guess a few people have at similar conclusions, seeing as how Facebook developer activity is down. Caroline McCarthy at c|net goes so far as to suggest that the platform has an expiration date, despite only being a year old.

Maybe if it does, then I won’t have to get these invitations anymore. That would be fine with me.