Why doesn't the Set function work on transform.position?

A little confused about c# with Unity. This doesn’t work:

void Update () {    		
	transform.position.Set(10.0f, 0.0f, 0.0f);
}

This does:

void Update () {    		
	transform.position = new Vector3(10.0f, 0.0f, 0.0f);
}

Why?

You have to use new Vector3 in C#. Refer to this thread, it has a pretty good explanation.