Yeah its hard to say why something goes "viral." I guess it is a combination of many things about the article and not just one thing.
At first glance, it appeared it was because it was a review of an Olive Garden, where eastern elites and "real" food critics would never review a chain..etc.
You are right it probably has to do with "Marilyn's folksy but latently passive-aggressive style that I think so charmed the nation," but you gotta admit after all these years it took the Olive Garden to garnish the attention.
I will say she is right in the fact Olive Garden is/was highly anticipated. (Its like us guys highly anticipating a Hooters.) Living in GF most of my life, people (ladies especially) would always talk about an Olive Garden..."If Grand Forks just had an Olive Garden." And the level of "chatter" for good or bad on a national level might be the same.
Maybe this is more to do with the power of Gawker....a site I never heard of.