There's a great band, Big Medicine, that I just saw in concert last week in West Chester, PA and their repertoire is such that the band "runs the fault line between old-time and bluegrass..." (from the notes of their 2nd CD, Fever in the South). If you're trying to understand differences between old-time and bluegrass, I think it is also important to understand the overlap.

IMHO, there is no antipathy here. Only constipation.

-Greg