Why Dose React Use Synthetic Events?

According to the docs, a react synthetic event is a

a cross-browser wrapper around the browser’s native event. It has the same interface as the browser’s native event, including stopPropagation() and preventDefault(), except the events work identically across all browsers.

Why is it important that the events work the same in every browser if their interface is always the same (as implied by ‘It has the same interface as the browser’s native event’)? Dose the fact that React uses event delegation make this nesessary somehow?