I'm pretty sure it's fairly common. Obviously, you have permission to store it on your ereader, although I would like to know what their rationale behind forbidding download and storage is -- or how they intend to do anything about it.
But yes, it's fairly common,
even though no one knows/cares, or so much as looks at that notice in the ordinary way of things.
The reasoning undoubtedly is the typical BPH hatred of ebooks.