Swamp,
Your point is taken, but a dobro is actually just one brand of resonator guitar. Like "Kleenex", I guess that it has become synonymous with the product type and the resonator is very often considered its own instrument separate from the guitar. Depending on the day of the week (or time of the day), I might do that myself. However, in this particular post, I was including Douglass in the broader class of guitarists. I understand those who'd put him in the separate class of players, but it's essentially a semantic distinction at the end of the day. Probably a little sloppy on my part, tho.