Showing the importance of identity in a mailing address is a bit ridiculous. 
Once again I will repeat: it's probably just a tradition.
Mail is addressed to addressee (a person, a company, etc) - not the address. Unsolicited mail/spam cases are excepted.
While it's true that from the sender/recipient's point of view, you're addressing it to a person, but in actuality, you ARE addressing it to an address, with the understanding (hope?) that the intended recipient is actually there. From the mail system's point of view, the name of the person/company is nothing but decoration. You can easily test this: send two letters to someone. On one, write their name, but no address. On the other, write their address, but no name. Guess which one will arrive...
If we had the actual ability to address mail to a
person, then all we'd need to do is uniquely identify
who the recipient is, not where they are. It would be up to the mail system to figure out where the recipient is and route it to them.
The closest thing we have to that right now are email and mobile phones: the address or number doesn't change as the person moves around.
Indeed, phones are a great analogy. Traditional land-line phones are like snail mail: the number reaches a
place, not a
person. Sure, you hope the person you want is there, but they could have stepped out. The number continues to be tethered to that location.