Google can't tell that something is instructions. That's not something they do. It may know that ehow has a lot of pages with How To on them, but it doesn't know if those are pages with step by steps for how to do something, nor does it know that Rotten Tomatoes has pages with Opinions and Points, and conclusions that make up a review.
For the sake of realism only: any basic supervised machine learning algorithm does that with proper labeled dataset. I have built many. I can assure you this is so classic that Google has it, that many other companies have it. And there are much better and accuratd solutions in place for combining all signals of this kind.
Well their move to semantic technologies e.g. Schema.org is a step in the direction of understanding these things better. Like if you mark up the page with http://schema.org/Review wouldn't you agree that they know it's a review?
Google can't tell that something is instructions. That's not something they do. It may know that ehow has a lot of pages with How To on them, but it doesn't know if those are pages with step by steps for how to do something, nor does it know that Rotten Tomatoes has pages with Opinions and Points, and conclusions that make up a review.