Concert stage layout -- who made who?

Last night I was visiting a friend to listen to his SET setup. It sounded very nice - kinda the polar opposite philosophically from my own system... but anyway.

We were listeing to Bave Brubeck's Time Out. I wondered after listening for a while about the soundstage placement of the musicians. The drums were on the right (in some tracks) along with the keyboards. The clarinet(?) and flute seemed to be in the left of center portion of the stage (that's not a political comment) while something else (I can't remember what it was) was placed far off to the left.

Generally nowadays with Jazz/folk/rock the drums are in the center/back, while the star/singer is in the front while the other status instruments are immediately to the right and left of the singer/star. Okay, so here's the question: did the layout of the soundstage dictate where people stood on the stage, or did the stage dictate the soundstage?