That's not true, actually humans are unable to distinguish differences over 300 PPI at approximately 12 away.
There is no visual difference in normal usage between a 720p and 1080p screen on a phone.
When you drastically increase the size of a screen to that of a large screened TV then the 1080p screen is much more useful, but on these 4.7" screens the only substantial difference between a 720 and 1080p screen is the power drain and strain on the processors.