Well Mike....

I've done a few sessions over the years and I'm gonna have to beg to differ...

I've heard lots of grumbling about what key we're in...

Hand a horn section a chart in B natural and it's just a matter of how many seconds before one of them grumbles "couldn't this ---hole sing this in C or B Flat...5 freakin' sharps..what the hell are we guitar players?"

Answering Brian...some keys work better for some instruments in terms of the mechanics of the instrument..guitars like sharp keys..E..A..G...etc..horns prefer flat keys..Bflat...E flat...F...etc...
Honestly..in Chicago you don't see many Capos..not in the downtown sessions anyway...it's changed some over the years but except for the "folk" crowd capos were a no-no..matter of pride.

Ahhhhh music...all different, all the same !

Bob Young