Well, historically it's pretty simple - Bolts cannot be used in an arc. They had to be fired straight for various reasons, and that limits range tremendously. The range of say a longbow came from both the bow itself and the fact that you could choose whichever angle you wished and it would still be an effective weapon. Firing at the optimum angle allowed a significant increase in range without a large drop in killing power.
The idea behind the crossbow was two things - it was simple to use. The first Point and Click interface if you will. The only downside was that it takes a long time to crank. But considering anyone strong enough to crank a crossbow could use a crossbow effectively it was a great weapon, and as the crossbow became more popular, at the same time so did heavier armors. A crossbow bolt would punch straight through even the heaviest of armor inside it's smaller effective range. Arrows would simply bounce off plated armor short of nearly point blank ranges. Ease of use meant it was easier to train large amounts of men with them, whereas a longbow for example literally took a lifetime of practice and training to be effective with, while it was in most situations a better weapon you could field anywhere from half a dozen to a full dozen of peasants with crossbows for the price of a single longbowman.
In our game their advantage is again simple, against heavily armored targets archers will be very ineffective. Against average/light armor archers will be more effective, against heavily armored targets crossbows will be more effective. For best results you will need a mix.
Last edited by Josh Warner : 02-20-2010 at 07:17 PM.