I'm sorry but the assumptions you make about hornbows are wrong. I KNOW for a fact that perfectly functional outer limbs can be made with just wood.
Ok. Nobody doubts that. But for what kind of bow? For a really powerful horn no? No. For the best wood bow? Possibly not.
The core is what gives hornbows their shape 
Fading the horn out on the belly will give better performance.
Apparently not, according to multiple hornbowyering cultures around the world.
Wood at around 0.65 sg or horn that is less stiff and 1.3sg......No need at all for bone....The outerlimbs only need a little sinew on the back and require no horn or indeed bone plates on the belly/sides at all. Wood is stiffer than both horn and sinew.
It is true that horn is less stiff than wood and has a higher SG. Nevertheless it is a necessary component on the siyahs of several different types of composite bows, as we shall see, because it is stronger than wood..
When you say 'whip tillered' I think you actually mean elliptically tillered.
Unfortunately there does not seem to be an auhority out there who has defined what a whip tillered bow is. You guys said the Dan Brown flight longbow I posted was not whip tillered, but it is more whip tillered than several bows on Google's image search engine, which are described by forumites as "whip tillered".
Why do you think that a bamboo core is lighter than a wooden core? It isn't. The bamboo used is actually quite dense....
It is considerabl less dense than the typical woods used for hornbow cores (i.e. maple).
Is it just because they are beautifully shaped that Turkish bows do not need bone plates?
Well, the Turkish siyahs (or kasan) couldn't use the bone plates, because their cross sectional area is so different from other bows. Instead, the Turkish bow siyahs/kasan are reinforced with horn and a liberal layer of sinew (thicker than on the working limb). This diagram shows the unique shape of the Turkish bow kasan:
As we can see, the kasan (or siyahs) have a strange shape. They are cupped near the belly, and have a tall center ridge, that looks like a "nipple" in cross section. This essentially maximizes the stiffness of the siyah by giving it both thickness and width, but with a much greater surface area -- less mass.
Nevertheless, it is clear this design would never be stable in an all-wood construction, it has to have horn on the belly and a lot of sinew on the back. The siyah actually consists more of horn and sinew, than wood. It even has a thicker layer of sinew than the working limb. Try carving a shape like that out of wood alone, and how far you can draw it before it detonates.
So while the Turkish bow didn't need bone plates, it most definitely needed sinew and horn....
