There are almost always tradeoffs when you get near the boundaries of cutting edge technology. More power = shorter battery life, bigger batteries = heavier laptops, faster CPUs = higher temps (and shorter battery life), dedicated GPUs and smaller cases = hotter laptops and noisier fans. SSDs = fast, but with speed degradtion when filled near capacity. If you think that at a certain price point you can avoid having any tradeoffs, I just don't think that is realistic. Look at many "high-end" products like sports cars, and they all have similar tradeoffs (or as some people here choose to call them, "flaws").
It is very clear that there are differences between the LG and the Samsung retina displays, wrt image retention, so I don't think there is anything wrong with people wanting to get the best screen available for the laptop they purchased. Having obvious differences in performance based on who sourced the components, and having the peformance of what you get based on luck rather than what you ordered is not acceptable in my opinion.
However, is it possible that the retinal display on the rMBP (even with the Samsung screen) has some differences with image retention compared to non retina displays? Well, it's quite possible there are some tradeoffs at this time, though the evidence of this being a problem with the Samsung screens is pretty minimal at this point. If there is a difference, based on everythign I've read it is a very minimal difference that only appears under very unrealistic use cases.
My point was that if you want cutting edge of technology but are going to be intolerant of anything that doesn't meet your idea of perfection even if it doesn't have any impact on your actual usage of the product, then I think you are being unreasonable and aren't the type of customer any company really wants to do business with.
Doesn't anyone's actual usage of their Dell or Alienware M17x involve setting their background screen to dark gray, turning it to max brightness and leaving the same static image the screen for several hours? I highly doubt it. I also highly doubt that anyone has even run this type of image retention test on any other computer besides the rMBP, so I don't think that we have any sort of fair comparison at this point to indicate what is normal.
Obviously, if it does affect your usage of the product, then you should report it. Image retention while using the coputer? Report it. Stuck pixels or bright spots? Report it. My main point it is a waste of everyone's time to complain about things that don't actually have an impact on you during real-world usage of the product.
Of course everyone is free to behave in the manner they think is appropriate.