Two different things DK and PW. The first left unwillingly while making the third difficult album proven massive MM, (actually he had recorded some parts and he had his photo taken for the album inner sleeve) while the second left after the no.1 hit album Love ove gold, so actually knowing what he misses. Some friction can be creative in a group, but everybody should accept this fact. DK's rhythm contributions in the first DS albums were fine but MM parts were more demanding. However if you listen to DK's solo efforts, they are keyboard heavy (or anyway heavier that the 2 DS albums). So in a way he might have been responsible for this change of sound, in a way.
As for PW, I think it is a variety of reasons, already mentioned here.
And of course, there are some things that can not be told, for various reasons and we can only speculate. But really I care more about the music.
Thanks Allen for posting1