Now the advantage of a PoS system, is that it's naturally resistant against a 51% attack. To attack a PoS eco-system, you must have resources several times the value of the eco-system, otherwise, you WILL fail. On the other hand, to attack a PoW system, you just have to buy enough hardware to overwhelm the current miners, which currently cost about only 10% of Bitcoin eco-system value. This is why there has been exact ZERO successful 51% attack on any PoS alt coin, while plenty of PoW alt coin has been attacked to death.
This is false, as you are simply internalizing the risks with PoS instead of externalizing them. You would simply need to hack 8 to 12 peoples computers(Nxt as the example since you mention PoS-
http://charts.nxtcrypto.org/cDistribution.aspx) or they would have to decide to attack the system themselves if they are coerced to or have some reason.
I am not suggesting that PoS doesn't have any advantages over PoW , merely suggesting that your claims are fallacious. If we make PoW more distributed and people adopted p2p pools Bitcoin would be far more secure than any PoS coin.