Hello, I've been following this thread and finally got a chance to test some of these things on my own new 2013 Air. Now, I have the 11" BTO i5 with 8GB RAM and standard 128 SSD so this is obviously not a direct comparison to your Ultra 13" model, but it should be close.
I have gone over the Air from back to front, top to bottom with a very detailed look at the hinges, corners, finish, etc. I have found no imperfections. (I was surprised about that since I have had it for about two weeks now, and it has been in and out of my bag every day.) So that should mean that it is definitely possible to get an Air that is physically all good.
As to the "Magic Mirror" effect you describe. I have turned the laptop off, stood in dim rooms, well lit rooms, gone out doors for direct sunlight tests and, overall, I would say the image is relatively flat. As I move back and forth in front of the screen, I notice a very very slight... maybe call it a hiccup in the image in certain places. Which indicates a slightly imperfect flatness. I have never noticed this while using it and I have done some marathon 5+hour constant writing sessions on it a few times since I got it two weeks ago. So, unless you are unsatisfied with even very slight screen-reflected-image-deformation, that should be possible to get a replacement that is good there also.
Now, as to light bleed. I am a computer consultant and have been working on laptops of all makes and models for over seventeen years. It has been my experience that most of them--if I had enough time to even test or notice such a thing--exhibited at least a little bit of light bleed when at full brightness on dark backgrounds. And often at even half brightness. I am pretty sure that's a function of where the light bulbs/light sources are in the LCD screen. This also goes for most LCD monitors.
I tested this on my Air by changing the background on my screen to solid White, Red, Blue, Green, Yellow, And Black. I then lowered and upped the brightness on each color, slowly until any light-bleed was evident.
With the black background only, I notice light bleed along the bottom edge when I get to the last three ticks of the onscreen brightness meter. But it really isn't bad compared to other laptops I have used/worked on. And since I normally use the laptop at 50% brightness, (Half way across the onscreen meter--I assume it's linear.) I do not notice it.
Also, with respect to the light-bleed at those final brightness settings, it does appear, for me, to be brighter in the lower middle. And the bleed extends maybe fifty percent higher in the middle as well--from about a quarter inch a the edges to a half inch high at the middle.
So, do you see the bleed at lower brightness levels? With other colors? If so, maybe it is an issue. Return it. Do you normally work at full brightness? If so, then you may just be stuck and have to deal with it.
Lastly, I have, in the past, with an iPhone been able to have the Sales people take it out of the box so I could inspect it prior to replacing it. (I had an iPhone 4 with dust under the screen and got it switched.) Is that a possibility with your Apple Store. Make them unbox it, set it up enough to use, and test/inspect it before you take it as a replacement.
Hope that helps!