Rob: I'll believe that when I see it. Yeah, I've read the anecdote about the BW that was left strung in a shop for years, and the owner says it didn't lose a pound of weight, etc.
Problem is, no one has ever truly measured a bow's draw weight before and after a 20-year, or even 10- , 5- or 1- year sit with the bow strung. And even if the effect isn't measurable, it still occurs. All of the materials used in building a modern trad bow have some elasticity, some more than others. Over time, under stress, there's going to be some compression of that elasticity. It may or may not be noticeable or measurable, but it occurs. Of course given that the effect is so minor, it's probably not worth worrying about.
But what about all the old recurves that have been sitting in closets for years that end up with bent/warped lower limbs? I suspect most of those were actually caused by improper stringing, but the popular belief is that it's caused from the weight of the bow acting on the limb over the years of storage. How would a strung bow be any different?