Kaleea, I couldn't agree with you more, actually. And Mark summed up my thoughts and feelings quite well. I love old-time music. Would I be a fiddler in an old-time string band if I didn't? But I'm more than a fiddler. I enjoy a good song, and I like backing up singers, as much as having other musicians backing me up when it's my turn to sing one.
One of the reasons, I suspect, that singers are less than welcome at exclusively fiddle sessions, is that singers put the song where it is comfortable for their particular voices. And just as often, that means impossible [HA! Aint no such thing.] keys such as Bb, or perish the thought Eb. At the risk of offending fiddlers everywhere, that's just plain laziness. There is no excuse for refusing to learn to play in singer's keys. It ain't that hard. And it ain't that hard, 'cause the accompanist doesn't have to do all the fancy stuff he or she is capable of to back up a singer. Put simply, simple accompaniment is best.
Next time try it and see what I mean. Go to a session and when it's your turn, announce "OK, let's do The Nightengale in 2 flats. Kick 'er off there, Bob." And see what pained looks you get. Sheesh :-(
Jim