Personally, I fly at least once a week and would not feel comfortable not flying for say 3 weeks. It's not good for the plane, either. But that doesn't come exactly cheap...
The trouble with examing the various silly rules is that one might never stop. My favourite one is the 3km min PPL visibility - one cannot navigate in such muck using the techniques taught in a PPL. This is not a "currency" rule but is probably much more dangerous than not flying for 3 months and then flying in a simple plane on a nice clear day.
I don't think the presence of passengers affects safety as such; only in that there are more people to kill in one go IF you crash.