Diablo – How does +% damage on weapons work

Weapons have become accessories in Diablo 3. Since the game is designed to prefer magic skill attacks over melee, the weapons work like your pants or hat—they add to your stats and attributes, though you may never swing your weapon as a melee attack. You can set melee to a hotkey if you want, though. In your example, yes, the bow and dagger are equivalent. Elemental damage modifiers are added to normal damage. It's all about raising DPS unless you desire an attribute modifier.

Yes, they are. The easiest way to check this is to find a weapon with a socket, since you can manually add +min and +max enchantements to them. Now add a Ruby to it (enhances damage by a certain range). You will see the DPS go up in the item tooltip.

Also, it worked the same way in Diablo 2, so it's likely that they simply just left it the way it was.