Yeah... that's not really how it works. Sony pays for PSN by diverting money away from what would be their profits. That was Sony's choice to make, and while you are indirectly paying for PSN because you are paying Sony, that's quite a bit different from actually paying for PSN. All of the profits that Sony makes are amortized and allotted in whatever way Sony deems fit, and Sony deems it fit to use some of those profits to fund PSN. If I bought a Ford Focus I'm technically paying for the research and development of the next Ford Mustang, but I'm not actually paying for the next Ford Mustang.
And, by the way, that's not what a "hidden cost" is. You would be paying the same amount of money regardless of whether PSN was free or not. The only difference is that it would end up going somewhere else. For it to be a hidden cost, PS3 games would need to cost more than the equivalent 360 game, with the excess money going to PSN costs, but without Sony giving a reason for why the games are more expensive.