at least since digital video

Right. Even back in the eighties UK broadcasters were "upscaling" American NTSC 480i60 shows to 576i50. The results were varied. High-ticket shows like Friends and Fraiser looked great, albeit a bit soft and oversaturated, while live news feeds looked terrible. If you've never seen it, The Day Today has a perfect example of what a lot of US programmes lookd like converted to PAL.