I have no idea about some of those other desktops, but all the basic moving parts are mostly necessary:

- logind because you probably still want lid/sleep events to work when at a VT

- gdm because you probably still want lid/sleep events to work while nobody is logged in

- desktop settings because different users may want different things to happen on those events

I'm a little confused as to why the gdm settings were needed, at least for me those only take effect when the greeter is actually open. And in GNOME the separate screensaver daemon has been removed, in part because it simplifies the whole equation.