While that may work in a couple limited cases, what the iPhone does is far, far more complex than just applying a blur. Have a look at the picture below.

Now whereas the rim of the glass and straw have issues (those could be fixed), you’ll notice a distinct difference in the blur that’s applied at different levels in the photograph. The foreground, as well as the subject is crisp. Then you’ll notice the sunglasses are a slight bit less in focus, starting with the bottom of the frames and moving to the top. Then the edge of the table and background are completely out of focus.

A single, universal blur couldn’t come close to the sophistication this kind of computational photography brings to the table.