I wonder, though. Is that due to the MMO players, or due to MMO developers trying to please everyone, all the time?
For the most part, I don't see individual players bouncing back and forth on forums asking for something only to turn around when they get it and ask for the opposite. I do see part of the player base asking for more elite, difficult content, followed by casual players complaining about things that exclude them. PvP players complain about PvE focus, and PvE players complain about their class getting balanced for PvP.
There are many choices that will naturally favor some part of the player base, and instead of deciding what kind of player they are making the game for, developers of many games seem to create a revolving schedule of which players they are going to throw a bone to, and which will get shafted, hoping that all of them will feel placated enough to stick around.