The commercial alarms usually employ a starter cutoff instead of a fuel or ignition cutoff for safety reasons, since failure of a starter cutoff system just means you're stuck where you are. Problem is that it's too easy to bypass.
With a fuel or ignition cutoff, it'd be much harder to locate and bypass, but it'd be riskier if not done properly.
Lot of the stereo and alarm places seem to do quick 'n dirty wiring, with cut and tape connections or Scotchlok, which I wouldn't consider reliable enough. Solder and heatshrink connections would be, but would take too much time for them. That may be why they only offer starter disabling.
You could wire in a mechanical kill switch, which would be more reliable, but the tradeoff is that it wouldn't be as convenient as one integrated into your alarm system, and wouldn't be the passive type alarm insurance companies require if you get discounts on your comp premium for that kind of stuff.
Back when I worried about the car more, I had a paging alarm which I liked, because it would let me know if the alarm triggered, while I was out of earshot of the alarmbut still wasn't too far from the car. People have different views about wanting to know if their car is getting broken into; I'm of the camp that wants to know now, not after the fact.. I haven't seen them on the market any more though; guess they've fallen out of favor.
Hidden kill, sticking with the standard noisemaker, and maybe pager; that'd do it for me.