Yes, 'smart' contracts are great until they actually have to interact with the real world, and suddenly they lose their automatic, unstoppable, trustless features.

So far it seems that the only true reliable ethereum use cases have been ponzi schemes and dice games, because these can be implemented completely in the system.

Ethereum's much-promoted gambling app, 'Augur', gets very messy when it comes to settling market winners. I wonder how they will cope with fixing wrongly-settled events, and who will foot the bill?

Yes, but it at least reduces your counterparty risk to trusting someone to deliver an accurate price feed, rather than trusting them to deliver a pile of money. There are various ways to reduce the trust in a single party, from simple multiparty voting to ambitious betting schemes like Augur.

If they used Oraclize (secured by TLSNotary), impossible to forge any data, it would be as authentic as Poloniex/Kraken's APIs say it is.

so it means trusting Poloniex/Kraken's API, so not decentralized and trustless.

it also means trusting TLSNotary