If they're aware of the issue with a few people, they're aware of it. That doesn't mean that it's an epidemic like these message-boards would have you believe. And the 3-week think I truly believe is just a shortage of parts, and that the fix is just a replacement with another screen. Whether it has a greater or lesser degree of yellow is just the luck of the draw.
Mark my words, this is NOTHING new.
I agree with you about the 3 week thing probably being unrelated to the yellow tinge issue, but this most certainly IS an epidemic. I've yet to see a 27" iMac's screen within an acceptable tolerance of yellow in person, and I've toured around local stores (seeing about 20 of them) plus owned 3 myself, and none of them were anywhere near as consistent as any other monitor I or anyone in my family has owned, including cheapo $150 19" LCD's. You can keep telling yourself its acceptable, but I'm going to keep getting exchanges until I get one at least as consistent as my Dell 2407.