As an experiment, ask a few people you know to name 5 blues guitarists. I would imagine that you would get pretty similar responses across the board - BB King, Eric Clapton, Muddy Waters, Buddy Guy, Stevie Ray Vaughan. A relatively boring experiment, sure, but interesting to note that probably no one you ask would name a predominantly acoustic guitarist.
Granted, there are arguments for the recency effect and for public exposure having a lot to do with why that group comes to mind first, but the point is that most of us picture the blues being played electrically and loudly. As we've been listening to concerts from the Ash Grove catalog we've gotten a taste of what the blues were like before their amplification, played by the guitarists that inspired the generation that is so well-remembered today.
This playlist features some tunes by the originals like Lightnin' Hopkins, Mance Lipscomb, and Sam Chatmon. Musicians who heard these guys at the Ash Grove, like Taj Mahal and Ry Cooder, are represented, as are others who were able to play like the originals, like John Hammond (the III, though most know him as "Junior") and Rory Gallagher. Tracks from Loudon Wainwright III and Steve Goodman provide examples of acoustic blues being used for comedic irony, while indie artists The Felice Brothers and Justin Townes Earle capture the spirit of the originals without imitating them directly.