It needs some kind of incentive to get people to sign the checkpoints.
PoS is better than relying on one developer to lock the chain.
The incentive is: it keeps their (bit|lite)coins from becoming worthless. When you have or control a significant portion of the total supply of coins, that is no small incentive.
If you control 1% of the coins, you can still rely on the other 99% to work towards "keeping your coins from becoming worthless", so you yourself don't have a direct incentive.
I don't understand what's the big difference between hashing power and financial power. They're convertible and therefore ultimately equivalent.
StakeCoin is a way to reduce the friction of this conversion and
decentralize the network.