I field stripped two brand-new S&W Walther PPK/s pistols at a dealer's yesterday. Neither of them had a passive firing pin safety. Their safety arrangements appear to be identical to previous Walther and Interarms versions; i.e., they are equipped with an automatic hammer block (which is good for one or two severe blows) but the firing pin is locked only the manual safety is on.Yes, it has a passive firing pin safety.
I'm actually in agreement with you here."The firing pin in the PPK is inertial. Considering the mass of the firing pin itself, it would be hard for the thing to build up the momentum to fire a cartridge."
You may think that, but a few folks have learned the hard way that it should not be counted on. The only real protection against firing from drop-landing in all attitudes is to immobilize the firing pin by leaving the manual safety "on".