If SlipperySlope succeeds in releasing his PoS spin-off with pre-mine proportional to the bitcoin unspent outputs, and if he has agreements in place with various crypto-exchanges prior to launch, and if the launch is well-advertised, what will happen?
All bitcoin users will instantly be awarded an equal number of bitshares. On the exchanges, bitshares will trade directly against bitcoins. If you have 10 BTC in your Cryptsy account, Cryptsy could credit you instantly with 10 BTS for free. That's what PoS is: shares created without any work requirement.
No, getting the coins for free happens because of the spin-off idea of basing the initial distribution of coins on a snap-shot of the Bitcoin block chain. Any altcoin that uses spin-off will give free coins, even if it uses PoW.
Similarly, the altcoins that have an initial allocation based on, eg, Icelandic or Scottish citizenship also give free coins, and again it has nothing to do with whether the currency is based on PoS or PoW. The initial distribution has to come from somewhere. It's always going to be controversial.