Guys - Apologies for the late reply, I'd forgotten I'd posted to this thread.
Al - I honestly don't know what the transition point is between darkening of the wood from the effects of oxygen and UV light and bleaching. I have seen this happen to a few pieces that were kept for decades in a sunny window sill, but I didn't have the permission (and probably wouldn't have considered) taking a little off of the surface to see whether this was truly the effects of UV (one would expect that if it's primarily due to light exposure that the effect would be very shallow). One comment here is that of the antiques I've seen pictures of that were "in the rough", I've yet to see a colonial-period antique made of mahogany that was bleached out. They were almost uniformly dark from oxidized finish, age, and in some cases, the effects of linseed oil application. Ditto for cherry pieces, and as one would expect, the opposite for walnut - these almost always seem to have developed a golden-brown type of surface.
Mark - Not all oxidation needs exposure to air, and not all changes to pigments are the result of oxidation. My guess would be that the pigments in cherry change regardless of exposure to light and air - it's just that light and air greatly accelerate the process. From the stanpoint of oxygen getting to the heartwood, I would expect this to occur over many years, as the oxygen can relatively easily diffuse into the wood's pore structure. These pores, after all, must run along the grain lines or the tree wouldn't have grown in the first place since water and nutrients must travel from the roots to the leaves. And a gas like oxygen can difusse through pores much more easily than water can.
However, there's another possibility. So far as I'm aware, cherry with a rich, red color has always been greatly prized. Cherry is a transitional species that forms the first hardwoods in a forest that's been cut over. And the extent of deforestation in the growth range of cherry was truly gigantic towards the end of the 19th century. I would expect that would've resulted in much more cherry being available in the mid 20th century, and it wouldn't surprise me at all to learn that cherry with less than spectacular color was simply turned into architectural parts rather than be cut for lumber or made into furniture. It might well be that what we see when we luck into the sale of a 70 or 80 year old furniture company's leftover "grandpa's stash" simply is the pick of the litter.