The gestures of silent era actors developed from the 19th century stage where the same kinds of antics (knuckle-biting, back of the hand to the forhead, staggering backwards, etc.) had developed, although accompanied by speech speech. These gestures had more to do with being seen at a distance than anything else. In the last decade of silent films, this style of acting had pretty much calmed down. If you watch dramatic movies from the '20s, you see a style of acting that is pretty close to what was used in the '30s with the early talkies. The strange jerkiness of the silents is an artifact on the projection speed chosen today for silents, many of which were shot hand cranked. Again most of the later silents used electric motors rather than hand cranking and seem as smooth as the early talkies.

In fact, the early talkies had their share of strange rhetorical florishes and mid-Atlantic accents to deal with, and sometimes seem more primitive to modern audiences than silents shot a couple of years earlier.