Well, in the future, the ones being returned/exchanged now for faulty displays will get new displays.
I think it's really hard trying to look for a perfect one now (I was very very lucky with my iPad 4... first one was absolutely perfect) as we don't know how big was the batch of defective screens.
Also, another advantage of waiting a few weeks for some service models to be sent to the Genius Bar is that usually these undergo a less rushed quality control (that said, the replacement iPhone I got once had a poorly assembled front panel which clicked every time I'd tap the upper right corner) and the chances of getting a defective one may be minor.
Then again, these are all guesses, but if you have a noticeable flaw on your display be it a stuck pixel or something else, DO GET IT REPLACED and be very firm and strict with the Geniuses about it. Don't let yourself get entangled in their "within spec" chit-chat, and if they start refusing to get you swapped, ask to see a manager and explain the situation. Don't be rude, but be very firm.
I find it absolutely ridiculous that some people say that we shouldn't expect perfection from these products. If we all had the same very high standards and expectations, Apple would be drowned with returns and they might actually DO SOMETHING about the ridiculous QC standards at Foxconn factories. It seems that most people prefer to live with defects for the sake of owning the product though, which is shameful.
Defective screens on £400+ devices are simply not acceptable especially when those same displays are one of their strongest marketing/selling points.