Retarding ignition timing lowers cylinder pressure. It changes the combustion phasing. Here are some representative indicator diagrams which help illustrate the concept. I'll have to see if I can find some good heat release charts as well.
The OP's question is perfectly reasonable, considering that Ford Ecoboost engines are running on regular fuel.
What you have to remember though is that those type of engines are specifically designed for low octane use. For one thing, they use a lot of charge motion (port masking etc), basically a restrictive intake port meant for low-mid rpm use, to help reduce knock. Also, exhaust manifold and valve timing configuration reduce residual gases in the combustion chamber to mitigate knock.
Now, recall the basic idea of the D-4S combustion system. It is a system based on a high flow intake ports, with comparatively poor charge motion. It's not designed for really high knock resistance, it's designed for high filling efficiency.