> You would get a different sound from the different types of security pins

I'm not sure that's true...it may be true, but it hasn't been looked into. Also 99% of security pins are in the driver pins which aren't the actual pins that are making the clicking sound against the ridges. Since there is a set of pins (key pins) between the ridges and the security pins that could also "dull" the difference security pins change the sound.

In the same vein, though, great locks can also use different springs for each set of pins which also may effect the sound.