It was established two years ago that deep linking is legal (beyond the fact that it the very basis of this thing we call the web). The original argument against deep linking was that one company could be hurting another by leading a user directly to some content or service without the user going thru the advertising laden pages between the home page and the payoff page. I thought that was b.s. when I first heard it because most/all pages from commercial web sites are drowning in adverts anyway.
The advent of printer pages directly linked to by a third party completely denies the host of the content of any possible revenue from that page view. If that practice becomes truly systemic, one of two things will happen; another law suit will arise (not likely due to a precedent) or, more likely, printer friendly pages will eventually contain more adverts.