I can only speak for the Standard/Mark I and Mark II. Their safety can only be engaged when the hammer (not striker) is cocked. When the safety in the S position it blocks the trigger but not the firing pin.
Firing pin safeties make a semi-auto about immune to discharging when dropped but at the price of a heavier trigger pull. Compare the trigger pull of a Colt 1911 Mark 70 to that of a Mark 80 with the firing pin safety. Lots of folks (including myself) have bypassed the firing safety on 1911 MK 80's to get an improved trigger pull.
The basic rule for these Ruger pistols is to not drop them once you have chambered a round. That being said, hammer fired semi-automatics are highly unlikely to discharge when dropped. The Ruger 22's are the most popular of all .22 handguns with many millions manufactured and I have never heard of one firing when dropped.
My concern is with the striker fired pistols that go to half cocked when a round is chambered and have no safety. After Ruger's drop problems with the LCP, I am pretty certain that that all follow on Ruger designs of this pistol have included a manual safety.
I had an LCP fire with just the slightest of bumps, not even a drop and this was after the Ruger fix to the problem.
John