I dont think that everything should recieve damage. Blunt weapons, like a hammer, arent going to become less effective after heavy use like a sword is. If you buy a hammer, its pretty much a life time investment. Ive never had to take a hammer in for repair IRL.
Regarding bows, they also should not recieve damage, in the sense that a regular weapon does. Bows should be all or nothing. E.G. a bow work fine untill it breaks, but it cannot be repaired. Any bow made in this era would have most certinely been made of wood, and if a wooden bow snaps, there would be no way to repair it. A new one would have to be purchased.
I think that a bows durrability should be determined by a roll. Every time the bow is used, a roll determines if the bow survives, or if it breaks. of course the chances of a break should be very low, somthing like 1/1000. A higher quality bow could have 1/2500 chance, and a superior bow would have 1/10000 chance.
Other factors could determine a bows durability as well, such as if a char uses it to block an attack, like raising it above ones head to deflect a swinging sword. This kind of usage would most certinally destroy a bow, but again a roll could decide this. 1/10, 1/25, and 1/100
IMHO, a system like this would be much more true to RL. Feel free to comment or point out any flaws you see in this system, as I would greatly appreciate them. (comments, not flaws

)
Edit: Also, it could be made that bows are gaurenteed to work for the first 100/200/500 pulls, so that a person wont be unlucky enough to have it break after 5 uses. That would bite.