Aside from the observation that police miss their intended targets 80% of time, this article is pretty stupid. He implores you to stay inside your house, but then goes on to say that your house walls offer you little protection. Dumb, dumb, dumb. Some cover is better than no cover depending on the type of cover, angle of impact of projectile, and discounting any weird shrapnel effects that could result. Really, this article has no reason to be in “Popular Science”. I was hoping for some detailed information about ballistics and its penetration capabilities through various types of building materials or something like that. Instead, he makes a bunch of contradictory assertions why you should do one thing, but doing that one thing really won’t result in a better outcome for you.
If you want to some useful information, you can view these USMC penetration tests.
http://www.youtube.com/watch?v=lprGoEpDXJQ
My understanding is that anything that reduces the energy of the bullet will reduce its harmful effects when it hits flesh or bone. Window glass isn't one of those things, unless it's inch-thick window glass.