No one ever said that it wasn't important only that the flight characteristics are not affected by "wind" ie: a plane doesn't stall easier down wind than up wind. Yes ground speed and track are an important consideration to navigation, like setting up for landing, and wind will determine how soon and quick you need to turn. A quicker turn requires more bank which puts a larger load on the wings which causes more drag and therefore raises stall speed and requires more throttle. That exact same control input will have the exact same effect on a calm day as well. By the way we do have ground speed indicators now (GPS) and our down wind turn proceedure has not been affected in the least.