It gives them flexibility. (Additionally, multisig transactions cancel all the risk as long as they can find a 3rd party trusted to make the decision)
The seller can still go first, if he's prepared to shoulder the risk. Then the buyer can send the money once they receive the item. This is the same as using paypal.
If neither party is willing to go first, they have to either use a trusted middleman (seller gives item to middleman, buyer sends money, seller confirms to middleman, middleman releases item), or multisig transactions (the same, except the middleman can't run away with the money/item)
The seller can still go first, if he's prepared to shoulder the risk. Then the buyer can send the money once they receive the item. This is the same as using paypal.
If neither party is willing to go first, they have to either use a trusted middleman (seller gives item to middleman, buyer sends money, seller confirms to middleman, middleman releases item), or multisig transactions (the same, except the middleman can't run away with the money/item)