The low notes + the range. Trace has a big range (and a gorgeous voice at that). That said, I suspect you're right about the audience. Jake doesn't really do much for me, he isn't the vocalist that say a Sundance was, and I don't think he sells the story, or connects to it as well as even a Red or Chris K.
It amuses me how much this board likes him, I suspect if he was on team Blake they'd be calling him out as a generic one octave country singer (which he is).