Comment 4 for bug 1376716

I am pretty sure the problem is that the NUCs don't have APM. Here are a few relevant facts:

There's a new poweroff module included in Syslinux 5, which seems to still be APM-only but worth testing on the NUCs:
   http://www.syslinux.org/wiki/index.php/Syslinux_5_Changelog

The submission of that change triggered a discussion about ACPI support:
  http://www.zytor.com/pipermail/syslinux/2013-February/019524.html

Turns out someone did provide an ACPI-based shutdown module:
  http://www.syslinux.org/archives/2012-March/017658.html
  http://www.syslinux.org/archives/2012-March/017661.html

There is also this very simple NASM implementation of a COM module that was reportedly submitted to FreeDOS:
  http://h30499.www3.hp.com/t5/Business-PCs-Compaq-Elite-Pro/FreeDOS-FDAPM-PowerOFF-Workaround-on-HP-8000-Elite/td-p/1140783#.VDVxlq0sfOs

It's somewhat annoying that there's not a module that will just DTRT and use APM or ACPI depending on what's there, but it should be doable.

There is of course the option of stopping the use of the poweroff module entirely, and using an ephemeral image that shuts down correctly regardless of whether we're on an ACPI or APM host.