Well, if its a dumb question I'm in the same boat as you. On my TS45000 ish car the doors do have a slight curve, but the outer sills do not so I need to make some adjustments. There is a vendor in Australia who is selling sills with curvature, but for later post 60K bodies. His earlier sills are flat. He thinks that was original - I suspect he's wrong.
I've asked around and haven't heard definitely if doors were ever flat - but I've come to my own conclusion that the main issue is having a good door/sill matchup regardless of curvature. If you have no mismatch there, though, don't worry about it I think.