That certainly is kind of a dark prospect. Random people a mixture of varying degrees of foresight, money, and luck, suddenly becoming the richest people on the planet.
Gates built an empire. Yet the Winklevoss' will eclipse his wealth if BTC goes up just a few factors.
I don't begrudge people their gains, I'm just thinking about the seismic shift in power.
I know humor is forbidden, but I laughed out loud at this anyway. I felt compelled to comment because this is a difficult joke to setup in every day conversation.
I think the point is that the only reason to transfer such a large sum of money is either buying/selling something or stealing. And considering there probably aren't many (if any) things one can buy with that many bitcoins, theft seems to be most likely scenario.
Another option: Perhaps the security of the private key of the old address was in question, so a new address was created with a new, secure private key.