I think the issue he was talking about, is what if I sent the coins to escrow, they sent the cash, and instead of sending me cash, they sent me some newspaper clippings that are roughly the same weight as the cash would be.

There seems like no way for the escrow agent to validate that the buyer of BTC actually sent the cash, unless the escrow agent receives the cash and forwards it to the seller.  This can create a certain counter party risk from the escrow agent.