I have a "5 series" and I took it to a Mac retail store today, because, like the rest of you, I totally tweak out on these sorts of "imperfections". The phones that didn't have locked sims were all "7 series" and were all less "washed-out" than my "5". However, I wouldn't say that the blacks were darker or richer. In fact, my iPhone actually seemd to show a truer full screen black than a "7" I tested it against.
I showed the "washed-out" (very slightly, and not even necessarily negative) appearance of my iPhone to an employee, and he guessed that they wouldn't return it. I asked him if his phone looked like mine, and when we placed them side by side, they were identical. I punched the code into his phone, and low and behold, it was a "5".
On a side note, I couldn't see any white dots on any of the "7"s and I've never been able to see them on my phone either.