"Image retention" or ghosting is temporary and will go away on its own, it is nothing to worry about.
I work in IT for a large graphics company, we have standardized on 15" MacBook Pros (Retinas) for all department laptops. In my capacity, I open every single Mac (laptop or otherwise) and image it for the employees so I see it in a sealed box to the employees' desks. I do not personally own a Retina MBP so I have no bias one way or the other.
Out of the several dozen or so MBPs I have set up and imaged, I have not seen a single problem with the Retina display--ghosting or otherwise. If anything, employees who have the Retina MBPs absolutely love them. My next MBP will probably be a Retina (My early 2011 is still running strong!).
As an anecdote, LCDs are not immune to ghosting. I've seen it on desktop LCDs that have been left at a particular screen for long periods of time (usually when imaging).
Seems like as you say, you hand these things out but you dont use them.
A simple search will reveal how widespread this problem is. Apple began replacing Retina MacBooks which had this problem, before they realised it was just too embedded in their supply chain to do much about. So now they say something along the lines of it being acceptable and running your screen saver for 20 minutes to fix the problem.
Sure, its not just Apple that this affects, though due to the demographic of Apple users, it certainly affects its users more.
Fact is, this is a problem which should not exist for anyone, and Apple should certainly be doing more to address this frankly anoying fault - and it IS a fault.
I never said that I didn't see it, just that it wasn't a big deal because it would go away on its own. I usually have the MBPs in my possession for a day or two, installing apps and transferring data, so the screens are always on full. As a rule, I turn off power management until imaging is done and use Casper for the imaging.
If it makes you all feel better, my first gen iPad did this, usually with the Safari toolbar, and it went away on its own if I changed the screen to something else. My current iPad (3) does it as well.
Honestly man, I truly don't see this as an issue unless it is affecting your workflow. Some people see a dead or stuck pixel as a problem but just about every computer I've owned has had one or two.
Buy it, use it, enjoy it for what it is, not what you want it to be.