lol I think constant jumping in MMO's has more to do with the button they choose to use for it in all MMO's! The Spacebar!
The spacebar when typing was designed to be the most accessible to the hands because you use this key the most to separate your words! It is far to easy to rest your hands and just accidentally start jumping! When you get excited your hands tense up and... Oops! you start jumping.
If ppl just moved their jump key to someplace else, or SE chose not to use the spacebar as the default jump button. This would help alot! However the standard has been set in thousands of ppl's mind that that is the place the jump key should be. If they change the placement of the jump key there is nothing to prevent ppl from just changing the key bind back to the spacebar for jump.
Ultimately, I think the majority of ppl's jumping is because of the key used to use it! Not because ppl want to unnecessarily jump all the time.