I wrote my thoughts in a comment to Tobolds post but I am going to be lazy and copy them here for my own records:
Why do we even have to justify our decision to stop playing a game for a while. Moving on is an entirely healthy phenomenon in my opinion and yet there seems to be a suggestion of treachery about it. It is no reflection on the quality of a game or its community that you have gotten bored and want to do something else for a while.
Perhaps this is a fatal flaw in the current mmo business model. If Blizzard or Turbine or CCP's business model is based on the assumption that I and my fellow consumers will sign up to their offering for life to the exclusion of all other forms of entertainment then I am sorry but that doesn't work for me and I doubt it works for very many others either. I want variety. No matter how good a game is I want to play more than one game in my life and that means I have to move on.
Here are a couple of suggestions off the top of my head for a more customer friendly mmo business model.
1. An episodic or time limited mmo that has naturally occurring end points at which people "finish the game" and move on.
2. Thinking big how about an "internet of mmos". An overarching virtual world network linking all of the various mmos together allowing you to move your characters between virtual worlds at will. Tadd Williams Otherland comes to mind (which incidentally is soon to be an mmo in its own right).
I admit I haven't yet figured out how the above schemes would help companies make higher profits but in the long run products that do what the customer wants generally beat out those that do what the company making them wants.