Ally1,
Aspect ratios, don't you just love 'em - obviously not. The two channels you mention do feature a lot of archive material which would have been originated 4:3.
4:3 material displayed correctly on a 16:9 screen should have the pillar boxing (both in SD or HD). By making it fit the width of the 16:9 screen you are either keeping the correct aspect ratio by zooming in and hence removing the top and bottom of the image or stretching the picture horizontally and making everyone wide and fat and making the aspect ratio wrong - watch an old 4:3 edition of Top Gear and be amazed at the oval wheels!! (and none of those clever 'stretching' modes work either - watch a plane take off and enjoy the wingspan mysteriously expand as it comes closer !). 'Just scan' will make no difference to the pillar boxing.
I can't really see the problem watching a 4:3 pillar box image on a TV the size of yours especially as that is how it should be watched. No amount of techno wizardry can get away from the fact that that image is a 'square' 4:3 shape (not even 'Sh-ambilight'), and doesn't fit into a rectangular 16:9 hole. Remember you are watching the approximate equivalent of what would have been a 49 inch 4:3 CRT. Hope that helps !
Wish I was still stuck in Cyprus and diving!
Rob Scuba