Consistent with WHICH USER even *IF* everyone uses GNOME... different users can set up different policies? Your point of consistency is moot. The power settings for the login manager are, by sheer necessity of separating "system/root" from "user", different. You can't go and allow every man and his dog who has an account on the machine to define its login manager power prefs just because their own personal prefs are that.

You do have a point in that they will eventually re-invent the world and frankly... LightDM is NOT lightweight if it's using Webkit. Webkit is massive. It makes GTK+ look like a short Sunday stroll around the block.