There is difference between Misty and May. Misty has nothing to do in the show. May is a coordinator and she has a very important goal.
..Which is why they made Misty an official gym leader, a reason to kick her off the show since she didn't do anything.
It sucks May is leaving though, I loved the contests and everything. Having something else to look forward to other than Ash's battling was a great way to enjoy the show more. Now since May is gone, who is going to do Super Contests? Anyone? I don't want a May-clone now.