However, as the value of BTC increases, the large holders are incited to diversify their investment (usually via USD), so the distribution gets more even with time.
Assuming they can continue to find greater fools.
It could be said that Bitcoin will either continually increases in value, or collapse to nothing. As soon as there is any protracted period of price stability, all the speculative capital gets withdrawn and goes in search in a new bubble (Litecoin perhaps). The only way to prevent that is an ever increasing price, but that's not sustainable, especially as Bitcoin is not making much progress in terms of merchant acceptance.