but if the bad guy removes the batteries, nothing will happen and this particular zone has been compromised.
I agree with Brian, it sounds right.
Are you concerned about this? Because it is not unique to X10. My point is your questions are universal, and you will probably get similar answers when applied to any other alarm system.
If your concern is breaking the glass and removing the batteries, a fix could be adding a glass break sensor to the window switch loop.
The "cheap' version is a mercury switch stuck to the glass. The idea being when the glass breaks the mercury switch "tilts" and opens the circuit, triggering the alarm.
The high tech version is a self contained battery powered device that is sensitive "to the sound of breaking glass". When detected the device opens the window switch circuit which triggers the alarm.