True, but isn't the whole point of an alarm system to draw attention to the thieves? If a thief can bypass the alarm system or other security measures, it may not look they are stealing the car. This gives them a significant amount of time before law enforcement can be informed and greatly lessens the chance of them being caught.

That's the whole point of an immobilizer. To prevent the typical physical methods (break window, hotwire ignition) from being accepted unless the security token is also present.

I don't think Porche et al are under any illusions their windows are rock-proof. ;)