It should be that way, tbh, but the problem is is that people can easily copy and paste the public address to see how much that address has.  That's a real problem in, for instance, Satoshi's case (if that person is still alive) because he has made his address public and people can see his coins there and if he moves them at all.  So, unless Satoshi just all the sudden wanted to create a mass panic in the bitcoin market place; it's safe to say that the total remaining Bitcoins in circulation are 20 mill instead of 21.

Having a protocol in place where there is no ability for people to see how much you have in your wallet or trace where one person sends to another person is a pretty important thing for personal security of your own wealth.