The tokens here are essentially altcoins, like ether or bitcoin. How would that be done with a simple, private database?
As you say, the key point of blockchains, like bitcoin, is that there is no central trusted entity. So, like steemit has done, if you add a trusted person or company, the main feature of the currency is wiped out and there's no point in having a blockchain in the system.
I'm not saying this model is foolproof, and perhaps you're right and steemit (or app specific coins) will never be a big hit because of that. My point was just to show an example of a different kind of business model / monetization strategy made possible because of the blockchain, and there will certainly be others.