Well, the other day I wondered vaguely to myself if that could be configured a bit differently. Sure enough, after twiddling my thumbs waiting for my printouts a few minutes ago, I discovered that it was set to 30 minutes... and could be set longer!
Now it will go to sleep after it's not used for two hours. That seems a reasonable compromise; if it's really not being actively used, it might as well go into power-saving mode, but it shouldn't shut down in just a half hour. That's too quick.