Merchants would have never come up with that on their own. It was forced on them with credit cards by consumer protection laws. Debit cards don't have that legal requirement, but consumers have come to expect it.
The point is it's a legal invention - introduced by the banks so that people would actually trust credit cards - it's not a necessary feature of a traceable transaction.
It's a feature of having a 3rd party as part of the transaction. A random merchant trusts Visa to ban people who abuse the system. And merchants are threatened by with being banned if they don't keep quiet about the occasional charge back. However with a pure digital currency there is no independent party, so all transactions are either provisional or finalized with the merchants and customers having total power at different parts of the process.
PS: I am not going to sue if some random website fails to ship a 200$ graphics card. So reputation becomes even more important, but only because fraud will also become far easier.
P2P currency doesn't preclude 3rd party (escrow) transactions. In fact, it will likely be a popular option for large transactions and it will cost less than CC/debit card security overhead.
the genius of the credit card system is that not all of its features rely on what programmers would think of as technical mechanisms. legal and contractual constructs can be highly effective.
Merchants would have never come up with that on their own. It was forced on them with credit cards by consumer protection laws. Debit cards don't have that legal requirement, but consumers have come to expect it.