1) while I love these silent films and find them hilarious, i do not believe they were the Golden age of comedy. I believe they USHERED in the true Golden age of comedy, the talkies of the 30s and 40s. The Marx Brothers, Abbott and Costello, Laurel and Hardy, Three Stooges, etc, etc. These films added witty, clever dialog to film, while still using the visual gags of the previous era.
A) Mostly visual, but not completely so. There are scenes where you see characters outwitting others. Ok, maybe that's still visual?? Hmmm...
In the modern era, physical comedy in film has de-evolved to bodily function bits or crotch shots. Not clever and rarely funny. There are a few exceptions. I think Michael Richards, in Seinfeld, was an absolutely fantastic physical comedian. Jim Carrey is also a good, modern physical comedian.
3) these documentaries and clip shows help educate us on the past and introduce new generations to the great comedies of our past.