You're only looking at it from the buyers side. What about the seller?
You can add escrow on top of BitCoin but it's hard to add irreversibility on top of credit cards.
There are several ways to do escrow. Look at ClearCoin for one example where you place your money in the trust of a third party until both sides agree the sale has gone OK.
But you can also set up BitCoin to support a form of escrow without needing a third party to hold your coins in the meantime. They only get involved if there's a dispute.
Chargebacks provide something a bit like escrow or mediation, except the CC companies always side with the buyer and not the seller - so it's not a very high quality mediation.
The reason people are told to never send via Western Union is because that form of payment is overwhelmingly used by scammers, partly because it's irreversible but partly because it's one of the few forms of payment that work in the parts of the world where the scammers live.