because nxt randomly selects stakeholders to author blocks but in a deterministic way. i know it sounds like a contraction but it actually works. what i mean is that you can often but not always predict who will author the next block. the often means that you can do all sorts of cool and crazy awesome things like match visas transaction load and make transactions that are instantly secure. the not always means that you can secure the chain even though you can often predict.
there are other advantages. its more secure than peercoin. with peercoin someone can save up coindays and use their savings to doublespend. the randomness in the selection of stake holders in nxt prevents this.
the concentration of stake means that nxt will continue to be a big gamble until more of those initial funds get spread out more evenly. but there are reasons to expect that it will, namely that it is in the self interest of the big stakeholders to do so, and it will probably pay off big time if the stakeholders do make the right choice.
check out my essay for a more detailed explanation:
https://docs.google.com/document/d/1E_ToOMG2l1XThx6YnyXEajXaf6H1k2yjq8XkAF0ScB4/mobilebasic?pli=1
