Comment 1 for bug 238555

Disk-idleing (aka "laptop-mode") and power states are quite separate things.
https://wiki.ubuntu.com/PowerManagement

Since ubuntu by default ships with laptop-mode-tools (thus disabled) which handles all the things associated with disk-idleing,

(like mount options, hdparm options, low battery exceptions, disk-idleing on AC when on the road, etc.)

laptop-mode-tools will handle it.

The ubuntu package does not work yet as well as the debian package, though.
Package laptop-mode-tools needs to put scripts into pm-tools directories. #244844

(The current laptop-mode disk-idleing approach seems to be a left-over from before the ubuntu-laptop-mode package was droped for laptop-mode-tools.)

Also package acpi-support is still preveting much of laptop-mode-tools working.
#244833 #244831 #244832 #244839 #244836 #244838