You're right that it is not necessary to play the previous games. Playing Silent Hill 4 made me interested even more in looking into connections between characters (even if they were not necessarily present in the previous games and only mentioned for example in a newspaper article). I would love to mention some examples, but I will not do that in case I spoil anything important :D If you're afraid of playing Silent Hill 4 because it could spoil some major events from the previous games, don't worry, that's not the case. It is still a unique experience. At the beginning, I didn't even notice some of the references and to be honest, you can understand the plot without knowing the stories from the previous games.