It's something that Ben told me when I was asking about 'hush puppies'. He said that that term was specific to one gun and Vietnam reference rather than an overall nickname for any silencer. Then went on to tell me that weapons that discharged below sonic level (subsonic) took silencers, but those more highpowered (such as a Barett .50 would need a suppressor because the bullet being fired is travelling at supersonic speed.
That make sense?