You'll always see the authors doing exactly what they say not to do. Stephen King is a big one on that. He says not to use a lot of words or go overboard on adverbs, and such, and then when you read his books, he's very verbose when he really doesn't need to be. With POV, it's more for someone who's beginning to write. It's a whole lot easier to keep track of one person's POV than it is to keep track of something like 15 different POVs. Sort of like the difference between any book written in first person, and a George R R Martin book, or a Robert Jordan book. The more POV characters that are introduced, the more difficult it gets for the reader to follow along. Plus, it's pretty rare that you'll find any author that changes POV character in the middle of a scene.
I'd say the main reason that you do see authors doing what they've said not to do is simple. Basically, it comes down to the fact that you have to know the rules before you can break em. When I first started one of my fantasy pieces, I started in first person. When I started a rewrite in third person, I had three POV characters. With the most recent rewrite attempt, that's changed to something like 5. For me, it has to do with becoming more confident in my writing and being able to handle multiple characters clamoring in my head to have their say.