How it should work is there should be more now classes with higher str requirments.That would be more realistic. As you said, though, the main problem is the high base damage for bows.
there is also a skill to increase bow speed and some bows have speed 6 on them.The recuperation time isn't going to get less than zero, though, so a speed bonus on the bow just means it is a little faster early in the game (before you max the Bow Expertise skill).
This means that a bow is doing 50% more damge than the highest damage 2 handed sword in the game at the same speed.Is the base attack time for swords and bows the same?
Why put something like this in the game because killing everything in 3 seconds isn't what I call fun.Probably the same reason Frost on a weapon ignores the target's resistances, so always freezes it.
I tried a Frost sword briefly, which was also not fun (as soon as I hit anything the fight was effectively over, I just had to wait for my character to hit enough times to kill it). At least with an over-power bow, fights are not fun and short.
Another point with the bows is you can stand face to face with a melee monster and still keep firing.With a single character game, the alternative would be forcing the player to keep running away (perhaps realistic, but not much fun) or switch to a backup weapon (which could perhaps be seen as a hassle).
BD had speed penalties for heavier armour. That wasn't enough to cause a realistic penalty for an archer (or mage), but maybe DD2 will be better in that regard.