That’s like saying bitcoin could be a Money table on my personal database. It’s not the same at all. These coins are unique, wont be tampered, work on exchanges, and don’t depend on you trusting the startup that created it.
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.