http://www.ufogreyinfo.com/infoonthezetasgreys.htm What if the Greys are from the distant future, devolved beings who need to invade the past to sustain themselves. This would also tie in with Isaac Asimovs Light Years, where the men of metal who serve a giant brain invade the past and turn everyone into men of metal, while the brain harvests the biological. Sort of like the Cell from DBZ where Frieza is the Grey Alien killed by time traveler from the future, but more likely the Greys are from the future, but we have knowledge of such things and our governments deal with them. H.G. Wells envisioned a future where in a 1 million AD, everyone had become a grey alien.

Without a doubt, the Grey Alien is the most media friendly type and has become the common symbol for aliens, the common type we are familiar with. Shows like American Dad get us used to the idea of Greys living among us, The government allowed abductions from Greys and works with them in underground bases as well. South park had an episode where Aliens from the future invade the past just to live there.

It may be there are just from Zeti Reticuli, even so, that's not to say they aren't the distant future of human evolution on their world, and even ours if we proceed along a certain timeline.