I just received my pg278Q and out of the box it has 2 dead pixel...
It seems that to allow warranty your screen should have a minimum of 5 dead pixel as all other monitor from asus, I do not see special rule for "premium one"on the website.
All my previous monitor (dell, viewsonic) were having a zero defect pixel policy out of the box, and they were not at 800€.
I'm currently waiting answer from asus currently, they told me to send multiple photos for the moment.