I wonder if anyone here has experienced or has insight into this.
I saw it in San Francisco a few years ago when a friendly group of _amateurs de Bourgogne_ I taste with met for a holiday dinner at a fine restaurant with a high-profile (Master) sommelier who despite his cordial general help with arrangements for the several wines (he also knew some of the diners already), did not decant a magnum of 1985 Clos de Tart as requested, and when challenged, asserted that one is not supposed to decant Burgundy. (Some people who've enjoyed it longer than he has find Pinot sensitive to sediment and by no means badly affected by decanting shortly before service, that's their basis for doing so.)
More dramatically, this surfaced in New York at (again) a very respected restaurant where a sommelier refused to decant a 1985 Bonnes Mares (Roumier) magnum for an importer I know who has _comprehensive_ experience with Burgundies and had spent serious money himself on this one. The same thing happened there with another magnum of the same wine, but this time to Roumier himself. This is extraordinary and implies a policy, a dogma. These are moderately aged, special Burgundies on special occasions, and the people ordering them know what they are doing.
None of us has seen this in comparable ordering in France (I received an appetizing list of Burgundies happily decanted on request or automatically at Les Millesimes in Gevrey, Troisgros, Rostaing in Paris, Ecuson in Beaune, Lameloise, and elsewhere). That experienced correspondent added "Oddly enough most people agree that an old or very old wine that has been decanted right before service may improve in the glass for a time. If it is old wine, it will usually head down after half an hour or so, though some will keep going and a few will crash in just a few minutes."
Comments on this policy? -- Max Hauser
(Off-topic: Messrs Williams, Lipton, and implicitly Hoare, you might already have seen my "1982 Leoville" posting of 23-May, but if not, it contained responses to your earlier remarks.)