When POS is implemented at launch, and it is implemented properly, it works. Implementing POS midstream is a mess. Look at the coins that tried this, and see where they are now. Hell, look at most of the coins that started POS, and failed when POS started kicking in.
That aside... lets say POS was implemented. Like TamiLee said, people hoard. Coins will not move. And for what... 2% per year?
I don't know... I've just seen enough POS implementations that failed miserably. Maybe I'm just that grumpy old man telling the kids to get off my grass.
-Fuse