I followed most of the math but the part right before

multiplying together the conditional probability of each variable given the values of its immediate parents. (If a node has no parents, the probability table for it has just an unconditional probability, like "the chance of an earthquake is .01".)

has me puzzled. The variables used aren't explicitly mentioned elsewhere in the article, and while I think they have some conventional meaning I can't quiet remember what. The context let me make a decent guess, but I still feel a little fuzzy. Otherwise the post was pretty clear, much clearer than the other explanations I've seen.