The idea for PPC-like POS coins is to make a parallel chain. Eventually you'll succeed in winning against the main chain.
Ok, so you're going to buy a loads of coins and then
grow a chain of your own. And once coin operators get a whiff of what you're doing,
they will resort to automated checkpoints and eliminate your fork.
I'm sure it's a nice hobby though.
I have been hearing about that sort of attack for months, but nobody tried so far (at least not publicly... which probably means it does not work...)