I beg to differ. They're different, and offer another set of compromises. I got a set of a fairly hard compound, and whatever change in rolling resistance there is drowns in the other random factors influencing my commute. Time door-to-door is the same.
They do ride hard though, and are a bit squirrely on cobbles. But certainly flat proof.
Softer compounds are supposedly worse in terms of rolling resistance. But for a commuter I'd rather take 5 known minutes extra than the unknown hassle of a flat.