> The inhibit api of gnome-session lets you do just that
> as far as desktops are concerned, the policy belongs in the user session
Not if this policy affects all users of a computer. The computer shouldn't autosuspend if another user has important applications running that block suspend.
> Not sure what 'odd daemons' you have in mind
If you haven't peeked into your process list lately, here's a few:
colord, upowerd, udisks-daemon, rtkit-daemon, polkitd, accounts-daemon, NetworkManager, modem-manager