In reply to cb_6: Ramblin dave has got the essence of it, one of the fundamental differences between trad and sport is the nature of any uncertainty. With sport the uncertainty is (nearly totally) confined to your physical ability, with trad other areas of uncertainty - quality of gear, mental ability with boldness etc come into it as well.
Old fixed gear that is doubtful has this uncertainty so is generally accepted as valid for new trad routes until somebody does without them - hence using the old aid bolts on Baron Greenback. The acceptability of new fixed gear is location dependent; e.g. on natural gritstone - never.
I wonder what the situation would be if the old bolts on BG were stonkingly solid - unlikely with any such old fixed gear - I suspect that they would still be used but there would be more ethical pressure for somebody to then do a bolt free ascent so that they could be chopped.