If you want things in the block chain to represent shares (ie: you want the management to count your vote come agm time or pay you a dividend) or you want some farmer to deliver you some corn then they (the management or the farmer) becomes the point of failure. You're relying on them.. the fact that there's a block chain that says they should do something is completely irrelevant. They might as well just keep their shares/corn orders in a very ordinary spreadsheet.
That's true for corn, yes, but not stock, which can be traded electronically, automatically and securely.
And for corn, that is analagous to selling a coffee or a car for bitcoins. You are relying on an external point of failure.
So what if the corn (or coffee) is never delivered. Having one element outside the scope of the project does not eliminate the utility of the bitcoin approach.