Ok...since it seemed like maybe I didn't give enough info for people to advise me from my earlier posts, I decided to just go look at a bunch more ipads on my own. I looked at maybe 15-20 of them but I'm not sure the total really. What I found was interesting so I thought I'd share.
I saw DQ, DLX, and DN6 ipads (no DL6?). I encountered 6 with either no or very minor bleed, all of which were DLX. All the DN6 had substantial to severe bleed. The couple DQs I saw had moderate.
I also encountered a few other problems, though, all of which I might actually consider *more* distracting than backlight bleed. They were as follows:
Color Temperature: Based on this thread, I had gotten the impression that there were basically blue-shifted and yellow-shifted screens. This was not what I encountered. Instead, I found blue-shifted screens, that I felt were a little washed out too. I encountered yellow-shifted screens as well, that were maybe a bit dimmer than the blue-shifted. I also encountered red-shifted screens that were similarly washed out. Lastly, I encountered more or less neutral screens.
Interestingly, 5 out of 6 of the 'good' screens were _not_ of the neutral type. Both of the no-bleed screens were kind of red shifted. DN6 models usually were the blue type it seemed. DLX I encountered neutral, red, and yellow. I did encounter red shifted screens that had noticeable bleed, as well as yellow shifted. Several bleeding screens were pretty neutral as well as nicely bright.
Falloff: Every screen I saw had some amount of falloff, including models I've seen during other excursions. The amount and shape varied. Typically, it was towards the left side if held in portrait orientation, home button on the bottom. One no-bleed screen had substantial falloff as a gradient towards the left side along the vertical. The other one had severe falloff outward from the lower left corner. The neutral 'good' screen had minor-to-moderate falloff on the _right_ side, oddly enough. The others were similar to the vertical-oriented no-bleed screen, some more or less severe. Some bleeding screens had small amounts of falloff.
Color shift: Possibly related to falloff but seemed to vary independently, I saw shift towards yellow, blue, and red. The neutral 'good' screen had some shift towards yellow in the corners, and it seemed like a bit of neutral-to-blue across horizontally but I wasn't sure (I didn't spend hours examining these things!). The no-bleed screens both had some shift. Some bleeding screens had no detectable shift.
Overall: The combination of the above factors could affect contrast, which could affect perception of sharpness and I at least found added to eye fatigue due to differential brightness across the frame.
As a result, I went out looking for the probability of getting a no-bleed screen, and discovered that "optimal" is really a neutral, no-to-minimal bleed, low-to-no shift, minimal falloff screen. In other words, a rare bird indeed. Only one of the samples even vaguely exhibited this and it still had problems. Of the various attributes, I felt neutrality was probably the most important, followed by falloff, but that's just me.
Now you guys have tons of other things to look for!