Anyway PoS limits the partecipation to an oligopoly, while PoW is open to everybody, without distinction.
That's an illusion. PoS coins have no more an oligopoly than PoW coins. You think mining 0.1 LTC per day via PoW is worth anything? Spending $300 on a GPU to mine versus spending $300 on a PoS coin itself... I'd say the PoS coin actually redistributes itself better than the PoW coin.
Well, unless you're NXT of course. Then I agree with you.
I really like PoS, but I feel it could use a few tweaks to become "perfect" still.