Why do you want this information?
It is interesting to compare your amount to other ones 
To do that, you will need everyone to use only one address for all their coins and nobody is doing that. Why would I put all my coins in one big bag and advertise to the world that I am filthy rich? It would be stupid, because you would be painting a target on your back for hackers and thieves to hunt you down.
Let's say somewhere in the future, some steroid induced super computer, finds a way to encrypt private keys, which addresses would you think, will they be going for? Developers will strengthen the encryption if this happens, but by that time all the big addresses with the mother load will have been targeted. ^grrrrrrr^
I read some answers that they would just like to see how many bitcoins are their in a wallet and they are just interested. But if you have malicious intent, the scenario you laid out could also be possible. They can go down in the list and see if they can "break" private keys. So for me, the list doesn't have a purpose.
I wonder if one of these addresses might belong to a guy who has totally forgotten that he bought/mined bitcoins back in 2009/2010.
Well that's possible, We read countless news about some random guy who bought bitcoins at a low price then totally forgot about it. Then suddenly remembers he has stash someone only to find out that he already thrown his pc laptop. I believed that some of them are really lost bitcoin in oblivion.