The problem is that if merchants are told to just trust transactions that haven't been confirmed, then there is the possibility that the losses will be quite high. The face that only a small percentage (zero?) of transactions are currently double spending isn't relevant, because no one out there is trusting transactions until they've been confirmed, so double-spending isn't a viable exploit.
If you set up a few "is this transaction pending" servers at well-known locations and only accept a transaction when it shows up at a majority of such locations (and no conflicting transactions show up at any of them) your vulnerability to a double-spend attack is so close to zero as to be negligible. (For the applications for which people routinely take credit cards or use cash.)