POW requires trust in the community of block signers also, which in most cases means a few large mining pools and farms. Delegation and apathy are not unique to proof of stake, and it's best to design the protocol to account for realistic expectations about the role such factors will play.

Obviously in a POS network the distribution of stake is critical, and the distribution of Steem is quite centralized. That fact encourages even greater voter apathy in this network, but does not necessarily indicate a flaw in the consensus protocol itself.