The irony is that Apple does not design or produce LCD panels.
They don't produce them, but they sure as hell employ a large number of people to design them, and they invested a huge sum of money in their manufacturing partners to build the production capability. At the end of the day, that's essentially the same thing. The part of Samsung that builds displays is not the same group of people that designs them, and once you've made that division, you start hurting brains when you try to map it out.
That's what's complex about most large companies--"Samsung" isn't really one company. It's a huge array of different companies sharing the same name and overlapping in leadership. That's why they can have both a great relationship with Apple and a highly contentious one at the same time.
LCD manufacturers (LG, Samsung etc.) do not call their own panels "retina" and they sell them to everybody.
Not exactly the way it works. These displays aren't going in any other products any time soon and maybe never, depending on who licensed what from whom in the co-venture.
This wasn't an off-the-shelf purchase like many other components.
When the same panel gets installed into Apple device it magically becomes "retina".
That's less than clear because it's too soon to tell. Apple uses the term to describe a family of its high-resolution displays, and only time will tell how the rest of the market shakes out.
It could end up being like Sony's "Trinitron" displays, which used aperture grille technology that other manufacturers had access to, either by working with Sony to license and rebrand it or by developing similar means on their own. Other manufacturers making high-ppi displays using similar technologies can come up with their own brand names. Maybe we'll see Samsung "InvisiPixel" displays later this year, or maybe they'll stick with the QXGA shorthand, which communicates less information.
"Retina display" could also end up being used more broadly to describe any display technology from any manufacturer conforming to pixel size under 1 arcmin at typical distance.
I have had my LCD TV (and before that my CRT TV) for years and was not aware that it was retina even though given the viewing distance and pixel density it clearly qualifies to be called retina.
And that's illustrating the point: a term was needed to contextualize the difference. High resolution isn't new. High density is new, and it needed some sort of name. HDTV came about for the same reason--a term for products to distinguish them from the rest of the market.