In my case it's the HP multifunction device driver
Usual problem with HP ... the hardware's the best so you have to buy it, pity about the attention to detail that isn't lavished on the software.
I get similar (not identical, earlier versions of Windows) behaviour which is down to HP drivers - if the network printer is turned on then windows shuts down normally, but if the network printer is turned off then there's this delay on shutting down any computer on the network.