Nival isn't stupid after all....
Look, how many heroes can you hire in one turn? 7-9 (I might be wrong, so correct me if I am.....)
And that means that if 8 players choose to hire heroes in multiplayer, each player can only hire 1, and that means you can't order more heroes, because you can't hire from another faction, and your own are already taken....
And now tell me, who plays with only one hero? No one. Everyone has at least 2-4, or even more... so that's why you can hire heroes from other factions in the castles....
I think I've answered your question. I'll close the thread in 2 days. If you have any more questions, or rather, "Some thoughts," then speak up....