Well those are addresses not wallets.  Unless you intentionally consolidate coins a wallet will contain a large number of addresses.

So for example someone had a wallet with 1,000 active addresses and the average balance per address was 10 BTC they wouldn't be even on the top 100,000 address list but they would still have 10,000 BTC.  Another thing to consider is that most likely when a single large early adopter sells off a large amount of BTC it is being bought up by multiple parties so distribution to a larger base occurs.

As pointed out above most wallets use a new address for each tx and don't reuse addresses, and send all change to a new address so unless you intentionally "send coins to yourself" to consolidate it you won't end up with a few large value addresses.  The main purpose for those massive addresses is offline storage.

Say you are MtGox and users have deposited 500,000 BTC.  You know that on your highest volume day the net outflows (BTC withdrawn - BTC deposited) is 10,000 BTC it makes absolutely no sense to keep 500,000 BTC online where they can be stolen.  You can move 400,000+ BTC offline likely in single large tx and you may not need to move them to an online (hot) wallet for months, maybe years.  If the exchange remains popular and growing you may never need to move those coins online ever again. 

There are a lot of entities which act as a bailor (google it) for other people's coins.   Exchanges, the Bitcoin trust, Bitcoin ETF, Bitpay, and yes the SilkRoad (now in the hands of the DOJ).  Those entities don't "own" the coins they are holding them on behalf of someone else.  Now they certainly can steal them (and people should be aware of the counterparty risk) but for example if one (or dozens) of those top 500 addresses is MtGox cold storage address it doesn't represent the wealth of a single person (or even single company) it represents the entrusted wealth of thousands maybe tens of thousands of users.