It seems that in NHL playoffs, referees tend to be a lot less likely to call a penalty. What is the reason and is this an official rule in the referee handbook or is it more of an unspoken rule?
I think there is some kind of unwritten rule that refs do not want to change the issue of a match with a bad call in any direction. That rule hits even harder when in playoffs, and even harder when its a win or go home game, especially game 7.
There is no official directive that I know of, and there is probably some studies that have been made to confirm or deny what you are advancing.
My opinion is that they still officiate the same, but those missed calls, that happen ever so often, are magnified because of the importance of the match.
I believe that actual penalty rates are not particularly different between the NHL regular season and NHL postseason. However, the heightened nature of the playoffs means every missed call is magnified. Also, common refereeing complaints of "reffing to the score" and "not wanting to make a game changing call late" are just as common in the regular season and the playoffs. There is obviously no rule in the rulebook that states different standards for the playoffs.