"HomeGrid Forum, a global, non-profit trade group promoting the United Nations' International Telecommunication Union's (ITU-T) G.hn standardization efforts..., today announced new liaison agreements with the Demand Response Smart Grid (DRSG) Coalition and Z-Wave Alliance."
Liaisons generally mean more politically than practically. In this case, you can see that Homegrid, the HomePlug wanabee, has hooked up with Z-Wave, the Zigbee wanabee who is also HomePlug's partner in all things smartgrid.
Notice that both HomePlug (IEEE 1901) and Zigbee (IEEE 802.15.4) are both in the IEEE family. Homegrid is a United Nation standard and Z-Wave is 100% proprietary specification which makes it a bit surprising that they teamed up.