As said, it was carry over from live.
On live, damage bonus was directly added to your damage... ie a weapon with a damage bonus of 8 would never hit for less than 1+8.
This made weapons with low delays infinately more powerful, especially at the end game. Damage bonus was unresistable damage.
I believe wizzy balanced the melee game before damage bonus was available for EQEMU, and didn't feel like changing the basis of the server just to add this crap. Then again, I am talking out my ass. Like the American Liberal I am. <3