As you probably know by now, PS Plus is mandatory for most online gameplay, and now Sony has revealed that about half of all PS4 users have PS Plus accounts. PS Plus was a big factor in determining if one wanted to buy a PS4, since it is now a requirement.
On the PS4, unless you were playing free-to-play games like DC Universe Online or Blacklight Retribution, a PS Plus account would be required for multiplayer online play. This was not a bad thing since it would mean more resources put into the occasionally malfunctioning PlayStation Network. And now, with more than four million PS4 consoles in the hands of gamers, about half of them are subscribing to the service.
This number is a threefold increase compared to the PS3, but it also means that half of the PS4 user doesn’t care for the service or apparently want to play online enough to pay the price. For only $5 a month Sony offers a lot of added value to the console. I suspect that after a year or so, we may see that number go much higher as users discover some of the games on offer.
Source Geek