I hit the jackpot the other day and found steel capped volleys! Black ones at that! I actually cannot describe how excited I was! A lot of places I work at have policies requiring tech'ies to wear steel caps as part of their OH&s and I usually make my crew where them regardless so now I can wear steel caps and still look cool!
Ehh....you've hit the classic issue right on the head.
Steel caps do not a safety shoe make.
The integrity of the whole shoe is much more important than just the caps.
Say something hits the edge of the cap and ends up on the material just behind it, if that material is thin and the object is sharp you are in serious trouble.
Thick leather(real or synthetic) and steel caps make a good safety shoe.