Bill. I would not say "a VERY real difference... Bluegrass is analogous to Irish session music...".

I mostly play in Irish sessions but have on occasion tried to play in both bluegrass and old-timey sessions and I have found the old-timey has got far more in common with Irish in terms of the music, the way it is played and I think in terms of the players themselves.

Irish tempos are strict in the sense that everyone try to play in time with each other but that's it. In a session I would argue there are limits either way but there are no strict rules as to how fast or slow a piece should be played or how the tune is expressed. Let's not forget, Irish music itself has a variety of styles - contrast a slow lilting Clare style with a fast Donegal style...

In an Irish session, a common etitquitte is to take the tune/set at the way the person who started it off did although there is sometimes a little bit of "settling in". In that respect and in my experience, I would suggest that old-timey sits in between Irish and bluegrass.

Jon