I've read a few interviews where MES talks makes an analogy of himself being like a football manager and feeling the need to "rotate his squad". He's also said stuff along the lines of seeing The Fall as something that needs to constanty change and move forward. Also, I can't imagine him being the easiest person to work with for long periods of time. Personally I've been really impressed with recent Fall stuff; I thought Fall Heads Roll was a great album - I've not heard the brand new one yet though. I saw the latest lineup a couple of months back in Birmingham and I thought it was one of the strongest Fall shows I've been to in quite some time.
I found this interview with Ben Pritchard (who played on Heads Roll) about how he left the group. I found it pretty interesting, as it kinda shows another side to the story:
http://www.visi.com/fall/news/pritchardint2006.html