为什么要使用事件而不是委托变量？

class Program
{
static void Main(string[] args)
{
Pub p = new Pub();
Sub s = new Sub();
p.NumberChange += new NuberChangeEventHand(s.OnNumberChanged);
p.DoSomeThing();
p.NumberChange(100);
Console.ReadKey();

}
}
public delegate void NuberChangeEventHand(int count);
public class Pub {
private int count;
public NuberChangeEventHand NumberChange;
//public event NuberChangeEventHand NumberChange;
public void DoSomeThing()
{
if (NumberChange != null)
{
count++;
NumberChange(count);
}
}

}
public class Sub {
public void OnNumberChanged(int count)
{
Console.WriteLine("显示：{0}",count);

}
}