Kirk, bendy handle bows spread the strains along the entire bow. With less strong woods or woods that are susceptible to maladies, like locust is to fretting, a bendy handle can relieve the strains. Bendy handle bows are also traditional through out history, ie. the English and Welsh war bows which bend is the arch of a circle and the Native American horse bows. I would imagine that the first bows were all bendy handles. It was a guy in England(I think) way back when named James Buchanan(the finest bowyer in London, "Longbow" by Robert Hardy) that developed the "Buchanan dip", Making a stiff handle with fades into the limbs. If I'm not mistaken before this most bows had bendy handles.
"The Buchanan dips is one such area (also known by the more modern term of "fadeout"). The dips are that transition area that graduates movement from static handle toward bending limb. It is the area on the belly side where the handle dips down to the working limb. The dips must be accomplished with much finesse. Make them too long in relation to bow limb length and you place unnecessary strain upon your limbs. Make them too abrupt or dramatic and you risk increasing hand shock or creating a hinge from a concentrated compression point. Make one longer or weaker than another, and the bow will not balance in your bow hand as you draw it." (Dean Torges, The Bowyers Edge")
Also, Kirk, we are talking about wood bow building as far as bendy handle bows are concerned.