Im starting to think that they all have this "issue" and that those who say they don't have ghosting are not checking the right way.
1. Set desktop background to dark grey.
2. Make sure in energy settings auto dim and sleep is set to never.
3. Open safari and go to google and leave the page on for 5-10 mins.
4. Press comman+H to hide safari and check for ghosting.
The ghost image disappears after about a minute.
I think you may be right. You have to do the test at full brightness. At first I thought nothing was "wrong", but if you look VERY VERY closely at the gray background (if you have Google+, where the profile icon was or where the Safari search bar is) then you can faintly see it.
Could someone who claims they DON'T have ghosting perform that test exactly as written and take a macro photo of the upper right corner of the screen? Color discrimination can be different among people so it may just be that some people see it and some don't.