Well, in that case calculating the sample mean of a dataset is machine learning too. So is sorting a list alphabetically. Regardless of whether it's supervised or unsupervised, how can you speak of machine learning if the metric is fixed before seeing any data? PageRank is human learning: people look at a bunch of pages they want categorized, figure out an intuitively appealing way to categorize them, and then encode those rules in an algorithm.

Edit: after thinking about this a bit more, I guess you could in fact think of e.g. k-means clustering as just a very advanced form of descriptive statistics, perhaps not fundamentally different from calculating a mean or a kernel density estimate. And in that sense PageRank would be unsupervised learning too, but it still feels to me like that's obscuring rather than clarifying how it works?