If you own a Beretta I'll defer to your knowledge, as I do not. I had thought the safety locked the slide.
On the M1911 (and all its cousins), Browning Hi-Power, Ruger MkI/II the safetly also locks the slide.
On a Baretta/Taurus 92, you can pop the mag with the safety engaged. Ain't no way in hell to clear the chamber without first disengaging the safety. It's a slide stop that flips up.
I don't own and haven't used any of those, so I defer to you on those models.
As far as the Glock and the H&K, well, there are "safeties" in the firearm - the Glock's is on the trigger, and the H&K is on the front of the grip. I guess it depends on what the meaning of the word "safety" is. ;-)
Bullpuckey. Glocks don't have an external operator-controlled safety, but they do have redundant internal mechanical safeties.
"Safe Action" System
The "Safe Action" system consists of three (3) automatic independently operating mechanical safeties which are sequentially disengaged when pulling the trigger and which are automatically re-engaged when releasing the trigger.
Without actuating the trigger it is not possible that a shot is fired.
The revolutionary trigger system consists of:
Firing pin safety
Furthermore the "Safe Action" system provides a constant trigger pull weight and a constant trigger travel from the first shot up to the last shot. GLOCK pistols are safe when dropped, when they receive any other abnormal shocks and are fully functional at temperatures from -40° to +70° Celsius.
The GLOCK "Safe Action" system has revolutionized the handgun industry and has been widely adopted by law enforcement and other official users as well as commercial and competition/combat shooting areas due to its simple, fast, safe and reliable application.
The main advantage of the GLOCK "Safe Action" system is that is has no external safeties. Because of this, the user can fully concentrate on the tactical tasks required whilst being in a stress situation and does not need to think about any safeties to be deactivated.
So very wrong, go to Glock's site and learn for yourself.
Besides, mechanical safeties are only as good as the safety between one's ears. The babysitter blew it.