about 40% in:
"Because of all the arguments above, we can safely conclude that this threat of an attacker building up a fork from arbitrarily long range is unfortunately fundamental, and in all non-degenerate implementations the issue is fatal to a proof of stake algorithm’s success in the proof of work security model. However, we can get around this fundamental barrier with a slight, but nevertheless fundamental, change in the security model." —Vitalik Buterin, saying the quiet part out loud
Security model in PoS = trust the rich. Some like having masters, whatever floats your boat.