I did see some electronic payment discussion which can be sent or refunded like a bank card. PayPal may already have a hold on secured online payments in a marketplace but there is no escrow. Let's assume that you want to sell something for $1000 USD (or EUR or GBP) for an item on eBay. The buyer sends the money and you ship the item, but the payment method was compromised (like a stolen credit card) or the item is damaged in transit. The agreed upon price or good is no longer valid.

Unfortunately, PayPal doesn't account for much that may happen after the payment has been sent. I recently purchased a small ticket item on eBay where the seller sent me the wrong item and I returned it hopefully in exchange for the item I purchased. However it never came and no communication from the seller. PayPal investigated and refunded the money within the hour which wasn't too much work but let's go back to the 1000 item. There would be a lot more investigating into the matter without any escrow account in the middle. This is just an example of course but it does happen in an online marketplace like eBay more often than one would think...