I would say singlespeed is a post 1995 concept/hype, so it fits neatly in the grey/dump category.
Except that the original "mountain bikes" were single speed cruisers made for going downhill, so I guess there must be room for single speeds and some downhillers in the retro world, unless you subscribe to the retro bike creationist theory. Personally I believe in Bikewinism, and the evolutionary process is what allows us to build retro bikes, like bike-eologists, carefully resurrecting frames and parts and re-assembling them in accordance with a point and time on the bikolutionary scale.
(The DH part is not for you Elev and neither is what follows spawned by your input, but the first Kona fully was sold in '94: Verlicchi frames also used by Ironhorse. I believe Intense started making fullies in '92.)
This said, a paleontologist wouldn't stick some bones from a dinosaur from one period together with bones from one existing a million years later and call it "true", and so in keeping with the usage of retro on this site, as many original parts, or (roughly) period correct parts would seem to make a proper retro bike. New components on an old frame would seem to be in conflict with this philosophy, however nice it is to breath life into an old frame.
However, one might contend that these bikes are in fact vintage, and perhaps only retro by default. When I lived in Vancouver, there were plenty of vintage clothing shops selling old clothes from the 70's and 80's. The clothes were from that era (vintage), not modern clothes reflecting that style (retro), and the cultural trend to wear old clothes would have been called a "retro fad", defining a movement within a culture that is inspired by a particular trend from a bygone era. A large part of a retro fad is no doubt inspired by sentimantalism, which also fits with many in here quite well.
This is only more semantics, however, and it's NOT my intention to start yet another debate as to "what is retro." When I found this site, I interpreted retro in the second sense, but understood that most of the bikes here fell under the first definition. I only have one that fits the first definition (minus the titanium riser bars...shame, shame, I know, but my back can't take flat bars and 130mm stems, and at least ti would be a period-correct upgrade.)
That said, I have no problem with the split. When the site was started, it was clearly done so with the first definition in mind, and that should be respected. I have no problem posting a picture of a classic or rare frame in a post 97 forum. Classic and rare are not necessarily retro by any definition. As I'm sure it's been pointed out, there are plenty of other forums to post totally modern bikes, like my Kona fully, which has no business being here...just like my 98% retro´92 Explosif has no business in a modern bike park.
So let's not all get are panties in a knot. We should keep retrobike as it was intended to be by it's creators (yes, I see the conflict with my bike-olution theory) and not try to change it on the basis of semantics. It was, after all, made with a specific purpose in mind, and we all get a lot of enjoyment out of being here.