It's not dead pixels that you notice; I have a hot pixel on my Retina MBP, and it's very noticeable. But Apple doesn't warranty a single hot/dead pixel.
I literally just came from my local Apple Store where I got my Retina MBP serviced for two clusters of hot pixels. The Genius had to look up the policy to see if it was covered, and came back saying that Retina MBP screens will be replaced for even a single defective pixel. We were both surprised.
I had an issue with a single dead pixel on a 3 month of rMBP earlier this year and Apple replaced it (the whole machine!) without any fuss. The Apple tech guy said (and this is pretty much the exact quote) "the rMBP is all about the screen, a dead pixel is not acceptable". Say what you will about Apple but their support is the best I have ever experienced. If I were you I would book an appointment at an Apple Store and get it fixed. I doubt you will have any problems. Backup everything first and be prepared to do a wipe and get a new machine if that isn't too inconvenient.
As others have said Apple will absolutely replace the screen for any dead pixels. I had mine first crappy LG screen replaced because of two dead pixels and they told me they'd do it if it was only one.
There are 14.7 million pixels on the iMac's screen. The definition of a retina display is you can't discern individual pixels at normal viewing distances, so unless you're sitting with your nose against the screen or are using a loupe, you won't be able to see a single dead pixel.
> The definition of a retina display is you can't discern individual pixels at normal viewing distances, so unless you're sitting with your nose against the screen or are using a loupe, you won't be able to see a single dead pixel.
Your conclusion does not follow from your premise.
Just because we can't identify individual pixels does not mean a single pixel has no influence. It shapes the overall picture.
If a single dead pixel is not visible at all, why have that pixel there in the first place -- working or not?
I just tested with my iPhone 6 (a 1334x750 px white picture with a single black pixel in the middle of the picture), and the single black pixel is definitely visible. A screenshot of the iPhone showing the picture in question confirms it's a single pixel on the screen.
For one it was never about "more pixels than photosensitive cells".
Second, the number of rods and cones has nothing to do with it.
The "retina" argument was about having smaller than discernible angular pixel sizes, which is true for the majority of people and normal viewing distances.
That's true on conventional panels, but the whole point of retina is that the pixels individually are smaller than the human eye can resolve. I'd be interested to see in practice. I suppose it depends how far your eye needs to be from the screen for it you count as retina in that way.
The inability to discern an individual pixel with the same color as its neighbors doesn't mean that the same pixel with a vastly different collor won't be seen. A single bright green pixel in a white window will still be visible, even if the edges of the pixel itself can't be seen otherwise.