This article is not scientific in any way. You cannot compare pixel density of a 32"-38" monitor to a 20"-24" monitor, and put them in a common denominator.
Retina effect is a factor of pitch size and distance of viewing. Now, you can't be viewing a 20" and 38" monitor from the same distance. Obviously this would be wrong. Now, why would a 38" monitor need a 220ppi to have the retina effect, when you will be viewing it at double the distance at least.
If we go by that article, our 65" TVs will need to be 16K, which they are not, and we still perceive them as retina, don't we - because they are so far away.