Paul
Unfortunately everyone has an ego. Art directors/designers all want to assert their right to improve a shot. They need to assert their contribution to the picture-taking proces. That is why they tend to look for the shot within the shot provided.
For this reason I find that my pictures get cropped and not always using the centre section! Also, amateurs who only have themselves to please can choose to frame a picture how they like but those supplying the graphic arts industry have to bear in mind that a shot might indeed be used either as a horizontal or a vertical shape. Only great art directors like Ron Brown would use a shot untampered with - and then go on to win lots of awards for Abott Mead Vickers!
That said, I find solace in the use of big dome ports and wide-angle lenses and have always put down corner blurr to the use of inappropriate and cheap dioptres on expensively designed primary lenses within compact dome ports. I have no problem withy edge sharpness with any of my present kit.
