My understanding is that the blockchain records every transaction that has ever occurred, and that, when we say there are x amount of coins at address y, what we really mean is that the blockchain records transactions in which the difference between the total amount of Bitcoin going to that address and leaving that address is x. In other words, it doesn't store the amount of Bitcoin at an address per se, but instead determines this by looking at transactions.
If my understanding of this is correct, then I don't understand how you are at risk of losing your Bitcoin if, for example, your hard drive crashes. The blockchain would still be able to tell how much coin was at that address, so all you would need to be able to do is prove that that address belonged to you.
If the problem is that the address goes away with the client and (most likely) the user didn't have their address memorized, then why not just add the ability to access the same address with more than one client? This way, if, for example, they lost their client on their desktop at home, they could still look up their address on their client at work, on their laptop, etc, and be able to recover the 'lost' coin.