It's a questionable choice. While the .22LR has been a favored calibre for gangland killings , such shootings are carried out at point blank range and the victim has to be shot several times in the head to ensure a kill. The preference for .22LR here is probably more to do with being quiet and portable, it is certainly not a powerful round. In one bizarre case a man was actually shot in the head with a .22 while sleeping and did not realize it; the bullet was only found when he went to hospital complaining of a headache (his wife later admitted 'accidentally' shotting him in bed).
Of course it depends very much on what sort of .22LR ammunition you are using, as there are many varieties in this caliber, ranging from subsonic heavy bullets to smaller "hyper-velocity" rounds and they all have different properties. But it's worth remembering that .22LR had not been adopted as a military cartridge, in spite of the large number of conscripts out there using the 'spray and pray' technique, as it is considered more useful against small animals than humans. That's got to raise questions about its use as a zombie-stopper.
Max Brooks recommends a .22 in his Zombie Survival Guide, but he's thinking more in terms of long-term travel through zombie-infested country, whereas the Wired article is referring more to a Zombi-style limited outbreak. Those .22 cartridges probably look a lot more tempting when you're considering trekking cross-country with enough of them to make sure to deanimate any walking corpses in your path.