I assume they sold some of it by now. But I see your point, does pos make the rich richer? Rich people can stake almost all their ether. since you can't move your ether for a long period of time after you stake it, staking is impractical for many. The first version of Casper will also include a minimum of ether to stake, though there are pools and they want too lower it over time.
Capital begets capital. The choice of consensus algorithm doesn't matter, as long as the system follows some kind of capitalistic economic model.