It's a question I've meant to ask (and will now I remember) in a separate thread, but for me it seemed that ME was the core illness and name, but it seems less so the more I read up on things.
So, you don't get properly tested for actual ME (in the UK at least), but put in the wastebasket, and if they can't be sure what's up, and you match enough, then without ME you still get put in the same wastebasket. So everyone is then misdiagnosed with CFS.
It's one of the odd things I've found here, that so many use CFS or CFIDS. I guess that's the success of the psych guys in muddying the water.
Here's a quicky answer on how the name-thing came about: