It's the difference between pseudonymity and anonymity. Saying that I've transferred B bitcoin to identity A doesn't tie that identity to a "real" person, it j

It's the difference between pseudonymity and anonymity. Saying that I've transferred B bitcoin to identity A doesn't tie that identity to a "real" person, it just says whoever holds A's identity (secret keys) can do other transactions with the bitcoins A holds. In practice this gets complicated as some exchanges require a valid government ID (drivers license say) and that's why these so-called "tumbling" services sprung up. The idea is that, for a small fee, you put X bitcoin into a pool with other people, and get (X - eps) back out and put into another identity of your choosing (eps being transaction fees). As long as the tumbling service doesn't get compromised so that the destination address can't be tied to the source address, this allows for a level of real world identity protection. Presumably even sending bitcoin from an identity that's tied to your meat space identity directly to another identity that you create provides a layer of protection.