Well, that depends. A multiuser setup may have an enforced power management configuration for the users, and in that case you may want it to match the greeter session. The real question is whether it's possible to make those policies equivalent or not, and if you've got two different implementations then the chances are it isn't.

There's a pretty solid argument for having a power management policy at the login screen, and that's that in a lab environment you probably want idle machines to suspend themselves if they're not being used for some sort of batch job.