> 1. A blockchain-based smart contract algorithm can very much check the price of a particular commodity on a particular exchange (fully automated enforcement).

Introducing trust issues with that exchange and what it decides to report to the smart contract that day. And that's the very simplest of circumstances, one data point from one source.

> 2. Parties can meet up and resolve the contract themselves (semi-automated enforcement that saves escrow fees).

So resort to non-smart way of resolving the issue, only the dynamic has likely already been changed as an automated system may have transferred funds already.

1. What if the exchange is down? What if the price is volatile?

2. You can meet up and resolve ANY contract yourselves. That doesn't save escrow fees.