It's likely the Winklevoss brothers have all their coins spread over many addresses. Their wallet will show 100,000+ coins but you can't tell because they are spread among many addresses inside the single wallet file. If they use a brain wallet seed they can create unlimited deterministic addresses but only have to remember one key, and you won't see large accumulations of coins.

What's the point?

Spreading the risk of loss by hack? And reducing their visibility as a target?

The reason is privacy. It's not going to spread the loss of a hack because if the hacker gets the wallet they own all the addresses.

One of the core developers theorized that memory corruption at the exact time you sign a transaction could lock away all the bitcoins in a single address. However this has never been observed. (remember every transaction spends the entire balance of an address and returns your coins to the same/or change address, if that change address has 1 bit wrong the entire balance would be lost)