I can chime in on this one.
The entire United States? They must not get around.
I've only eaten at Roscoe's Chicken and Waffles, but I've been there several times, both their Pico Boulevard location and their newest on Manchester Boulevard.
Is their chicken "that" good? NO! Is it good? Sometimes. Should it be in the Top Ten in the US? I don't think so.
I've had so much that has been better. The last visit I ordered white meat which I usually don't do and it was so dry, I had to douse it in hot sauce... not for flavor, but to get it down.
If talking the Southern California... Los Angeles and Los Angeles ajacent I find Mrs. Knott's much better than Roscoes. Then again so are the chains Pollo Compero, Pioneer and Louisiana Fried Chicken. http://global.campero.com/index.php?showPage=38 http://louisianafriedchicken.com/
My favorite at the moment is from the Philipine chain Jollibee: http://www.jollibeeusa.com/
From the inclusion of just that one out of ten listing of Roscoe's Chicken and Waffles, I'd say that those taking the poll don't get around much.
Roscoe's is more about Roscoe's than it is about the chicken.
Would I go back? Of course!