Of course, if you can keep all your trading in a closed system, that would be very difficult to impossible to tax correctly. But that's nothing intrinsic to Bitcoins. In fact, whatever else you can trade in such as gold, cash, collectibles, seashells or whatever, is probably more suited for avoiding taxes since you don't have to worry about the public ledger.
Bitcoin is the first store of value that you can send anonymously, digitally, and without involving central authorities. None of your other examples are as useful.
People put way too much emphasis on Bitcoin's public ledger. You only need one honest wallet/mixer like EasyWallet, a Silk Road account or a dedicated mixer like BitcoinFog to make your coins untraceable. Using multiple such services in a row means you are safe provided any one service didn't keep logs.