Thats true, I am sure alot of people do leave once they finish the story or stories if they try each class.
I prefer to stay not just for the endgame flashpoints or ops but for the chance to meet even more people than I have met now.
My first 2 weeks I had one person on my friends list and 2 weeks later it is over 50. Each one willing to come help me out on a heroic or answer questions I have about mmo's in general and knowing I will help them out with anything they have.
It just depends on the person on who stays and who goes.
Feel Free To Disagree.....Most People Do Anyways