I'm not sure why people are condemning you for returning the device to get a good one. I assume these people got a perfect one on their first purchase, because otherwise they would sympathize with the OP's frustration. Personally, I had to swap out the device twice: once because there was dust under the screen that I couldn't stop looking at, and once again because the screen on the replacement was half yellow and half blue and it was distracting every time I used it to read. The third doesn't exhibit those two flaws, though I haven't tested for retention or backlight bleeding or scratches on the casing or loose buttons because none of those issues would bother me enough to return it.
If two people walked into the store to buy the exact same device, and one was acceptable and the other person's had an obvious flaw, why would you expect the second person to simply accept it? Or worse, criticize him/her for demanding an acceptable device?
To those who passive aggressively suggest a move to an Android device: we don't know if the OP is invested in the Apple "ecosystem" and want to maintain some kind of consistency across devices. E.g., I wanted an iPad because I could use my calendar, iMessage, FaceTime, bookmarks, notes, etc. between my laptop, phone, and tablet. I would have no use for a Nook or Kindle or Nexus or whatever, even if the display was pristine.
Anyway, to the OP: my 2p is that you can continue returning it until they stop letting you return it, buy a different iPad model, or wait until the QC is better or the next version comes out. Also, I would assume Apple would want its customers to return devices until they're happy if it means retaining a customer. All the returned devices are probably turned into refurbs, and are sold again at a profit.