[dale_glass]

That only works so long the "car" resides entirely within the blockchain.

In the real world, there can be disputes after the sale. The property might have some horrible undisclosed effect. You might have stolen it. Or something else along those lines.

Securely swapping a bag of cash for some keys is solving the trivial part of the problem, and ignoring the rest.

The blockchain will do its thing and give you the title to a house infested from top to bottom with termites, but everything went according to the smart contract, so as far the blockchain is concerned there's no problem to be solved.