The distribution (factual) is right there in the link. I don't know who has how many wallets but since less than 2% of the coins have been mined there is basically no way it can centralize from here. I think the reality is setting in that bitcoin is a breakthrough, but it is by design neither novel nor irreproducible. So it doesn't make all that much sense to be paying 800 no 700 dollars each for them.
I guess it makes sense. The idea of bitcoin wasn't to make 50 people rich.
Why do you assume 1 address = 1 person.
MtGox cold storage address likely holds the coins for tens of thousands of users but in your "math" it is all owned by one person. The same would apply to every major exchange, eWallet, and bitcoin related business.
Likewise under similar math you would say 80% (or some asinine number) of all the dollars in the world are personally owned by four people named Chase, BofA, Wells Fargo, and Citibank.