Not sure what the minimum number for warranty claim is on the retina. On the classic 13 inch, it's 4 or more that are stuck (bright) or 6 or more that are dead (dark) or 8 or more in combination.
I'd guess, depending on the location of failures, that a lower number may sometimes qualify (but I think that's a judgment call?). Again, I'm not sure about the retina models.