Quite common, manufacturers say 5 of them or less is not classed as a fault. However OLED screens have even more issues, leaving a static screen on for an hour at moderate brightness will permanently damage the panel, horrendous technology, whenever i see an OLED screen i cringe. In a nutshell a dead pixel is a dead transistor.
Only tier 1 panels are guaranteed to have a perfect pixel array, Acer, Sony and Hewlett Packard. ive never owned a phone so not quite sure what the deal is there. Samsung though are an OEM for many other companies and a lot of them are cheap ass ones.
EDIT: i see you are talking about a monitor, in this case i would avoid samsung like the plague and buy an Acer or Asus panel.
i stupidly bought a samsung curved panel from currys last year (wifes mistake) the picture and colour was terrible, and the black levels were unbelievably poor. it went straight back.