Well I tried this with my pre-recall Ion when all this was going on. It took more than ten pounds of downward pressure. So knowing that, here is what's wrong with what you were told: If you have a normal keychain, you'll never have an issue. If you have 1/4 pound of crap on your keychain, and you experience an upward acceleration of 40 g, then the car could turn off.
Basically, if you were already in an accident, the car might shut off. But you still want to blame GM for it, because that's the popular thing to do, right?
Interestingly enough, there was a recall around the same time for the Takata airbags. These airbags were installed in many different kinds of cars, but since the most popular ones were Toyota And Honda, then it was the Takata airbags that were at fault, not the Honda or Toyota airbags. We can't blame them, because it's not popular to do so, even if it was covered up.
What does this have to do with the GM ignition switch? GM doesn't make the ignition switch any more than Honda or Toyota made those shrapnel filled airbags. But since they were put in GM cars, and it's popular to hate GM without prior thought, then it's GM's fault - not the fault of the vendor who made the switches.
I'm not defending GM here, I'm speaking out against the media swaying opinion on something they don't know anything about. Sorta like how most everyone on this site says auto reviewers are dumb for trying to nitpick the Mirage.