The HW has proprietary power management features that Windows cannot take advantage of. For the end user it's probably no big deal, but I think the commenter you replied to is right - power management is a delicate dance between hardware and software, and not all hardware is accessible from all software on every platform.
"Can't" and "won't" are distinct; if Apple doesn't want to write e.g. Power Nap drivers for Windows, Microsoft could certainly do it. (I'm surprised they haven't; Windows has the incentive to work well everywhere much more than Macs have an incentive to run everything equally well.)
