CFECO, do you have any proof of that? My tuft test shows attached airlflow all the way to the edge of the wheel well, and you know the Probe is FAR from the template in plan view.
The rockers are pinched in because
1. It looks good and stylists like it.
2. The side windows need to maintain their radius as they roll down into the door, curving in as they go down. The more tumblehome in the window, the more pinched the door. This gives the stylists more opportunity to sculpt the bodyside (see #1)
Many old English cars have straight sided doors. For example the Jaguar XK120, often regarded as one of the most beautiful cars ever produced, is in my opinion let down by its dumpy bodysides. Compare that to a Lotus Elise/Exige and you'll see the difference. The latter has a nice "wasp waist" in both profile and plan, while the Jag only has it in profile.