While I am muscially trained enough to transpose stuff on the fly, and I understand the need to change keys to fit vocal ranges, I am from the "the song was written in a certain key for a reason" school. One of my intital turn offs of early Phil and Friends shows was how just about every song had its key changed. This is an unreasonable comment but: I detest Sugaree in the Key of C, it just doesnt sound right!
I played with someone a while back who did Scarlet a step down (intro starting on A instead of B), it just lost all of its sparkle and shimmer. Scarlet just isn't Scarlet if it isn't in B..it loses that bright carribean vibe
Now some songs lend themselves better to transposition than others.
For example Let it Rock. I have heard Jerry do it in Bb when he had the Horns and do it in A with the Nicky Hopkins version of JGB and even heard an old version in B and another in C. That is OK. a 1-4-5 blues tune lends itself to key changes.
Jerry did change keys of a couple songs, but mostly for horn arrnagements.
In my Jer cover band, we will do road runner in F when the horn player is there (just like jer) or in E when he isnt (again, just like jer)
other than things like that Jerry usually kept things in the same keys through the years (with a few exceptions as people in this thread have noted)
Bottom line is that I personally favor doing songs in the main key they were either written in or played in the majority of the time. Just a stupid personal tic I have.
.......................................................have you heard the one about the yellow dog?