Well, I will be here for the long-term and have been here for quite a while already but don't consider myself jaded - do I count?
Yes, it's natural for expats to gravitate towards one another and sometimes you form friendships with people that you wouldn't have at home. I'm not taking that as a bad thing however - it exposes you to different people.
Meeting people is easy to do here, forming friendships is more difficult and takes time.
And as syngirl said, it gets exhausting (sorry) to meet someone & then have them pack up and leave after a few months. I think most people of my expat friends that I met 18 months ago are gone and of the ones that remain, I only know of 1 or 2 that have intentions of staying long-term. It's sad...