Since no one really seems to have taken notice of my last post I'll just say it again, this is all made perfectly clear in the in-game lore http://www.imperial-library.info/content/oblivion-manual-arms:
Arms have been made from many materials over the ages, and each material varies in weight, durability, and cost. These materials are here ranked in order of desirablility and cost, with cheapest and least desirable listed first: iron, steel, silver, dwarven, elven, glass, ebony, and finally daedric. Some armorers correctly observe that silver weapons are slightly less durable than steel; nonetheless, its unique ability to affect ghosts, wraiths and certain types of Daedric creatures is undisputed.
Bows can be made with laminated cores of the same materials. This provides a higher tensile strength and therefore greater power on the draw. The materials used in the arrow, particularly in the arrowhead, can affect its mass and penetration. Thus, the quality of the bow and of the arrow are taken together to determine the weapon's overall armor penetration.
Although not written out specifically, it can be assumed and also observed in many of the in-game bow models, that most of the bow is made from wood, along with ornamental parts and as stated here, a laminated core of the material in question. I'm perfectly fine with this description and would rather have it this way that having various different types of wood as pre-fixes, and while also taking into account that the rarer versions most certainly have also had some magic involved in their making and function, there's well enough explanation for the at first glance, "odd" material choice for bows ^^