WOL works by sending a 'Magic Packet' to a network device. The network adapter triggers a wake up event when a broadcast frame and 16 subsequent frames with the MAC address are received.
In the past, WOL could not be enabled on wireless networks because hibernation / sleep would cause the wireless card to turn off.
Wikipedia WOL requirements states:
802.11 wireless interfaces do not maintain a link in low power states and cannot receive a magic packet
The good news is that there is a new standard called Wake On Wireless Lan (WoWLAN)
According to Revolution Wifi:
- Integrated Adapters Required - The wireless adapter is required to be integrated onto the motherboard in order to control the power state
of the workstation (this category also includes mini-PCI and mini-PCIe
adapters). Newer motherboards and plug-in wireless adapters do not
have the required power connector and cable as some older systems
provided. Therefore, external adapters that are not integrated into
the motherboard will not be able to control the power circuity and
thus cannot support WoWLAN.
Because you are using a desktop, and WoWLAN is only available on wireless cards integrated into the motherboard (not running on the pci bus). If the following checkbox is greyed out, your card does not support WoWLAN.
Microsoft Support Document on WOL in Windows 8